Planning and navigating a ski tour can be complex. CalTopo places powerful mapping tools at your fingertips, but it’s more than just following a line. Which map layers are the best for scouting terrain? How long will your intended route actually take? Does your proposed trip for the day align with the current and forecasted conditions in that area?
Created in collaboration with the American Mountain Guide Association, Goretex NA, and Fischer Skis, the Pro Tour Tips: Trip Planning video series features helpful and bite-sized trip planning tips from professional guides for every step of the process. From the best map layers for avoiding the dreaded bushwhack to using the mobile app to navigate your plan in the backcountry, these tips will help you get the most out of your next ski tour.
Ready to dive deeper into trip planning with CalTopo? Make sure to check out the Winter Travel Series, where we systematically break down each step of the trip planning process and highlight the best mapping tools for the job. Whether you’re a mapping app newbie looking to master the basics or a veteran searching for tips to take your skills to the next level, there’s a little something for everyone.
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-02-14 13:13:172023-02-14 14:44:14Get More Out of Your Next Ski Tour
This is the first post in a 5-part series covering our favorite CalTopo layers and tools for planning winter backcountry travel. Each post will dive into a different stage in the process, from learning about the terrain to actually heading out into the backcountry with the mobile app. We will largely be focusing on the web app but many of the layers and tools are also available in the mobile app. Now let it snow!
Learning about Terrain
Learning about terrain can be a daunting undertaking, particularly if the area is new to you. Map layers like topographic maps, aerial imagery and slope angle shading can provide great insight into the natural features of an area from the comfort of your computer or mobile device. Let’s dig more into each of these layers and how you can use them to plan winter backcountry travel.
Compare Topo Maps to Get a Lay of the Land
A great place to start is with a topographic map, such as MapBuilder Topo.
Topographic maps like MapBuilder Topo can tell you a lot about an area.
This topo map is CalTopo’s signature base layer and it incorporates data from a variety of sources including trail and road data from OpenStreetMap, peak names from Peakbagger and relief shading based on USGS elevation data sets.
Contour lines and relief shading can reveal possible ascents, descents and travel routes.
Topo maps are helpful for visualizing the lay of the land. Using the contour lines, you can identify broad ridges or low angle slopes that may be good ascent routes. If you’re planning to ride or ski, you can also spot potentially good fall line descents. Relief shading makes these features stand out even more, helping you to identify them faster.
Topo maps also provide information on important features and points of interest, such as trailheads, logging roads, summer trails, and bodies of water. There is no one map that is the definitive source of truth about an area; rather, different maps display data from different data sources. Switching between topo maps and comparing the information present on each can provide more information about an area than just looking at one topo map alone.
For example, the image below shows the MapBuilder Topo and Forest Service layers (which displays official Forest Service data) in the same area. Drag the slider from side to side to compare the information present on each layer. How do the names of the peaks compare? Which layer shows trailhead locations? What features are present on one layer but absent on the other?
With CalTopo, you aren’t limited to just one topo map. You can easily switch between base layers or stack them on top of each other, allowing you to gather even more data about the area that you are interested in.
Visualize the Terrain with Aerial Imagery
While many topo maps include vegetation shading, diving into the aerial imagery for an area can really help you to learn more about what the terrain is actually like.
Finding the right tree density can be the difference between easier travel and a miserable bushwhack.
Even though much of the land itself is covered in (ideally) snow, aerial imagery, such as Global Imagery, can provide important insight about the underlying terrain for planning winter backcountry travel. Is a slope normally covered in rocks and talus or is it grassy? Where are the open meadows? Are the trees in an area densely packed or more spaced out?
If you are in the continental United States, a particularly useful layer is NAIP. Like many of the layers on CalTopo, NAIP is configurable. Changing NAIP to false color IR causes healthy vegetation to appear bright red, making it pop even more. This can help you to identify areas where the trees are densely packed (potentially presenting a miserable bushwhack) and areas where the trees are more evenly distributed (which could mean easier travel or more enjoyable tree skiing and riding).
If you are only viewing aerial imagery, adding the contour lines overlay or stacking relief shading in conjunction with the imagery can allow you to better visualize changes in elevation. You can also try stacking a topo map and adjusting the transparency to provide geographic context so you know exactly what peak or valley you are looking at.
Two layers can be better than one. Stacking aerial imagery with a topo map allows you to view the actual terrain with geographic context.
Dig into Slope Steepness with Slope Angle Shading
A popular year-round tool, slope angle shading is a visual overlay that uses a color scheme to identify slope steepness based on USGS elevation data sets, including high-resolution LIDAR data from the 3DEP program where available.
Each color corresponds to a different slope angle range. For example, red indicates slopes with 35-45 degree slope angle.
This overlay can provide great insight for planning winter backcountry travel: it can help you to identify gentle slopes that may be easier to ascend, manage avalanche danger, spot potential terrain traps, and more.
It’s important to note that slope angle shading can be an incredibly useful tool for increasing situational awareness but it is not the absolute truth. All slope angle shading has limitations, including errors in the source data as well as missing or creating terrain features based on the resolution of the underlying data.
Slope angle shading is most useful when combined with observations of the physical terrain, such as measuring slope angle with an inclinometer. We strongly encourage you to seek out professional training to learn more about traveling through avalanche terrain. Our partners at the American Avalanche Association and Avalanche Canada have some great resources to get you started or continue your education- make sure to check them out!
Try Different Layers and Combinations
As you start to explore a new area and plan your day, don’t be afraid to switch between different layers or try out new combinations. You may find that a topo map paired with slope angle shading to distinguish between gentle and steep slopes is really helpful for planning your initial route. Switching to aerial imagery stacked with shaded relief may provide insight into whether the route you planned is actually feasible given the terrain. CalTopo provides a wide array of base layers and overlays to choose from, allowing you to dive deep into the terrain before you step out the door.
Switching between different layers can reveal more about an area that just sticking with one layer.
Now it’s your turn! Are there any layers or tools we missed that you find particularly useful for learning about terrain in the winter? Question or comments? Leave them below.
Next week we’ll cover creating a map and planning your route. Until then, happy mapping!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-01-16 16:03:102023-01-24 13:46:11Winter Travel Series #1: Learning About Terrain
This is the second post in a 5-part series covering our favorite CalTopo layers and tools for planning winter backcountry travel. Each post will dive into a different stage in the process, from learning about the terrain to actually heading out into the backcountry with the mobile app. We will largely be focusing on the web app but many of the layers and tools are also available in the mobile app. Now let it snow!
Planning your route
As you learn more about an area, you’ll start to build your plan. Adding map objects (such as markers, lines and polygons) allows you to identify points of interest, potential travel routes, zones, and other relevant information. Overlaying your CalTopo map in Google Earth provides the opportunity to further visualize your plan in 3D and tweak it as needed. Let’s dig more into each of these features and look at how you can use them to plan winter backcountry travel.
Add map objects to build your map
What we call a “map” in CalTopo is actually just map objects that you have added at specific locations. Markers, lines and polygons are the most common map objects used for planning winter backcountry travel- let’s take a look at why you might use each of these types of map objects as well as some tips for getting the most out of them.
Adding and adjusting map objects allows you to customize your map to your needs.
Markers are a great choice for identifying relevant points of interest, such as the location of a trailhead, creek crossing, hut or decision point. If you add a marker along a line, the marker will show up in the terrain statistics or travel plan for that line. We’ll get more into tools like terrain statistics and travel plan next week, but for now just know that this can be particularly useful if you use markers to break a line up into legs- for example, you might add markers along a line showing an ascent route to indicate a potential lunch spot or where you might switch from skinning to boot packing on a ridge.
Markers designate important points, such as the perfect place for enjoying your pocket pizza. If you add markers along a line, they’ll show up in the terrain stats and travel plan for that line.
Lines are a useful way to designate possible ascents, descents and routes that you might want to travel. As you draw your lines, you can adjust how you are drawing them based on where you are trying to go. For example, if the first part of your ascent follows a summer trail shown on MapBuilder Topo, you can use snap to in order to snap the line to the summer trail as you draw. However, if you want to climb a broad ridge in the next part of your ascent, it might be a better choice to switch to clicking to add vertices or drawing freehand so that you can follow the contours of the land.
Switching between different drawing styles can allow you to tailor your route to the terrain.
Polygons are another common map object that are helpful for calling out particular areas. For example, you might add polygons to indicate common or local names for ski zones, such as the South Bowl, Silver Couloir or East Face. Since many zones can go by multiple names depending on who you ask, adding polygons with the name of the zone can provide a common language as you plan your day with other people.
While these aren’t the most unusual names, adding polygons to indicate the names of zones can make it much easier to collaborate and plan with other people.
Switching between map layers does not affect the position of map objects. As you add and draw map objects, you can change map layers as often as you would like to reveal even more information about a particular area.
Organize your map
Now let’s talk about the unsung hero of map organization: folders. Often overlooked, folders are organizational powerhouses. As you explore an area and add map objects, the Map Objects menu on the left hand side of the map viewer can quickly become overwhelming. Folders allow you to organize your map data in a meaningful way that can help make it more discoverable and manageable.
Compare the default folders (on the left) with the custom folders (on the right). Which do you think is more effective at organizing the data for this map?
How you choose to organize your data depends on the purpose of your map and what makes sense to you. For example, if your map displays possible ski tours in a particular area, you may organize the data into folders based on ski zones in that area. There is no wrong way to use folders- the key is to find an approach that works for you.
Visualize your map in 3D
As you start to build and refine your plan, exporting and overlaying your CalTopo map in Google Earth allows you to visualize your map in 3D. This can provide further insight into the nature of the terrain and how your plan stacks up.
Visualizing your CalTopo map in 3D can help you to hone in on the details of your plan.
If you are working with a saved map, you can use a KML network link to export your CalTopo map to Google Earth. The network link is a small file that tells Google Earth to keep requesting new KML files once every 10 seconds so that it will automatically update to show the latest version of your map. This gives you the option to tweak your map in CalTopo as needed, see those changes reflected in Google Earth and further refine your plan.
Didn’t mark the correct entrance for a couloir? Move the marker in CalTopo and a few seconds later, your change will show up in Google Earth.
Now it’s your turn! Are there any layers or tools we missed that you find particularly useful for planning your route in the winter? Question or comments? Leave them below.
Next week we’ll cover using existing map objects to learn about terrain and your planned route- that’s right, we’ll be getting into line profiles, terrain stats and my personal favorite, travel plan. Until then, happy mapping!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-01-15 11:19:142023-01-24 13:45:43Winter Travel Series #2: Planning Your Route
This is the third post in a 5-part series covering our favorite CalTopo layers and tools for planning winter backcountry travel. Each post will dive into a different stage in the process, from learning about the terrain to actually heading out into the backcountry with the mobile app. We will largely be focusing on the web app but many of the layers and tools are also available in the mobile app. Now let it snow!
Learning about your route
As you build your plan, you can use the map objects that you add to your map to dive into the terrain and your intended route. Is the line you drew for a possible ascent actually feasible to travel or is it brutally steep? Did you budget enough time for snack breaks and will you be able to get back to the trailhead before the sun sets? CalTopo tools such as profile, terrain stats and travel plan can shed light on these questions and more.
With this information, you can tweak your plan as needed to give yourself the best chance of a great day in the backcountry. Let’s dig more into how you can use these tools to efficiently plan winter travel.
Evaluate your route
As discussed in the previous post, lines are a useful way to designate possible ascents and descents. However drawing a line doesn’t tell you a whole lot about what it will be like to actually travel that route. Displaying the profile of the line allows you to visualize how elevation changes over the course of that line. On the web, the elevation profile is interactive. If you mouse over the graph, you will see a dot on the line itself that indicates where that spot is on the map. This can be particularly useful for pinpointing the locations of steep ascents or descents.
Moving the cursor over the elevation profile also displays the location of that spot on the map.
If you want to dig deeper into the terrain that a line travels through, you can also examine the terrain stats for that line. In addition to the elevation profile, terrain stats also displays graphs of slope angle, aspect, tree cover and land cover. Terrain stats can provide a more complete picture of what you can expect along that route– you can zero in on which sections have dense trees vs no coverage, what aspects you’ll be traveling through, and more.
Any markers you add along the line will also appear in the terrain stats. Looks like your snack break will be above treeline after you finish the steep part of the climb. Sounds scenic!
For example, based on the terrain stats above, you would expect that the first mile or so of your intended route to gently climb through a forest with well spaced trees. As you approached about 1.5 miles in, you would anticipate the climber to get steeper and the trees to disappear as you moved above treeline.
Estimate travel time
Having a realistic idea of how long a tour might take can be the difference between heading back to the car in the daylight or by headlamp. With shorter days and overnight temperatures that often dip below freezing, proper timing is a particularly crucial part of planning winter travel.
Displaying the travel time for a line provides a quick estimation for how long it will take to travel a single line based on the Munter Method for Time Calculation. The Munter Method is a popular method for estimating travel time through non-technical terrain that takes into account elevation gain and loss, distance and travel mode.
Travel time quickly displays the estimated time it would take to hike, bushwhack or ski a route.
However, oftentimes you want the big picture- how long will the entire tour take you? How much time should you budget for your ascent or the long exit with plenty of bushwhacking? And what about your snack breaks?
If you have a pro or higher account, you can create a more comprehensive travel plan. Also based on the Munter Method, travel plan allows you to incorporate multiple lines (such as separate lines for ascents, descents and traverses) and break those lines into legs by adding markers (such as for a transition point or snack break). You can then adjust the travel mode individually for each line, resulting in a detailed travel plan that provides an estimation of how long it could take to complete an entire tour.
With travel plan, each line gets its own section. You can break each line up into legs by adding markers along the line and adjust the travel mode to create a custom plan based on your tour.
Both travel time and travel plan can help you get a better idea of how long a trip might take. This can be incredibly valuable for planning winter travel so you don’t get caught out after dark.
Adjust your plan as needed
Based on the information you gather from tools like terrain stats and travel plan, you may find that your plan needs some fine tuning. Maybe terrain stats revealed that the second half of your ascent is unnecessarily steep or perhaps your planned tour is going to take far longer than you anticipated. Regardless of the reason, you can easily adjust your plan by either editing or modifying existing map objects or adding new ones as alternatives. Using tools to dive deeper into the terrain and your intended route ahead of time can go a long way in planning efficient winter travel.
Based on what you learn, you can easily edit a marker, line or polygon to adjust your plan as needed to meet your goals for the day.
Now it’s your turn! Are there any layers or tools we missed that you find particularly useful for learning about your route in the winter? Question or comments? Leave them below.
Next week we’ll cover learning about current and forecasted conditions for the area. Having a thorough understanding of what to expect in terms of snow, temperature, wind and avalanche conditions can greatly influence your planning for winter travel. Until then, happy mapping!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-01-14 14:20:292023-01-24 13:46:50Winter Travel Series #3: Learning About Your Route
This is the fourth post in a 5-part series covering our favorite CalTopo layers and tools for planning winter backcountry travel. Each post will dive into a different stage in the process, from learning about the terrain to actually heading out into the backcountry with the mobile app. We will largely be focusing on the web app but many of the layers and tools are also available in the mobile app. Now let it snow!
Learning about current and forecasted conditions
As you get ready to head out into the backcountry, having a good understanding of current and forecasted conditions for the area is essential. Knowing what to expect helps you to choose appropriate terrain and travel routes for a given day as well as pack the right gear. Map layers like avalanche and weather forecasts, weekly satellite imagery, and real time snowpack data make it easy to display this information directly in your CalTopo map.
Let’s dig more into how you can use each of these layers (as well as some other tools) to effectively plan for winter travel.
Get the avalanche forecast
A great starting point for learning about current and forecasted winter conditions is the avalanche forecast. Developed in close partnership with the American Avalanche Association, USFS National Avalanche Center and Avalanche Canada, the avalanche overlay displays real time regional avalanche forecasts from local avalanche forecasting centers in the US and Canada.
The avalanche overlay displays real time avalanche forecasts from local forecasting centers directly in your CalTopo map.
Each zone is color coded to reflect the current danger rating. Clicking on the zone brings up a dialog with a summary of the current avalanche forecast as well as links to the forecasting center and full forecast. We highly encourage users to click through to view the forecast details and discussion and dive deeper into the avalanche forecast.
The avalanche forecast provides information about any expected avalanche problem(s) and can be very useful for identifying appropriate terrain for the given conditions. We recommend that all users seek out professional training to learn more about traveling through avalanche terrain. Our partners at the American Avalanche Association and Avalanche Canada have some great resources to get you started or continue your education- make sure to check them out!
Investigate current and forecasted weather
Whether you are chasing the deepest powder or trying to decide if you should pack that extra puffy, it is also important to have a solid understanding of what to expect from the weather before you step out the door.
The weather shading overlay displays National Weather Service forecasts using a color gradient along with the numerical forecast for each forecast grid at higher zoom levels. You can choose between forecasts for 24-hour low or high temperatures, precipitation, snowfall, and max wind speed and gusts.
If you’re chasing powder, the weather shading overlay can give you an idea of where the snow is falling based on the color gradient. At higher zoom levels you can also view the numerical forecast which in this case is a little… dismal.
With this overlay you can easily visualize forecasted weather right in your CalTopo map.This can be helpful for choosing where you may want to go on a particular day as well as what to pack. However sometimes you need a more detailed weather forecast for an area. To do this, right click on the area you are interested in and then select NOAA Forecast from the dialog that appears. The full forecast for that area will open in a separate tab, allowing you to dig deeper into what to expect.
Sometimes you just need more information. CalTopo makes it easy to pull up the full NOAA forecast for a given area.
There is one weather factor in particular that is an especially important consideration for winter travel: WIND. Yes, the dreaded 4-letter word. It can have a big impact on snow, your terrain choices (which anyone who has been blasted by high winds on an exposed ridge can attest to), and what layers you decide to bring. With the wind plot overlay, you can view current and forecasted wind speed and direction directly in your map.
On the wind plot overlay, the color indicates the wind speed and the thicker end of the line indicates the wind direction. Looks like it will be a bit blowy up high in a few hours!
This overlay can help you to identify areas that may be sheltered from the wind versus areas that are exposed, spots where wind loading may be occurring, and more. As with any digital mapping tool, the wind plot overlay is most useful when combined with physical observations of the terrain, such as looking for signs of wind-drifted snow. Again, we recommend seeking out professional training to learn more about traveling through avalanche terrain.
Track snow coverage and depth
Snow coverage is often a big question mark in the early and late season. Is there snow covering the road to the trailhead or has it melted out? How far am I going to have to hike before I hit the snow line? Is a particular couloir still holding snow?
Available to pro accounts and higher, the Sentinel Weekly layer can provide insight into current and past snow coverage alongside all your other mapping data. The imagery for this layer comes from the Sentinel satellite program, which captures imagery of every spot on Earth from the same angle every 5 days. It has 10-m horizontal resolution which is good enough to zoom in on an individual snow patch or find the snow line.
With the Sentinel Weekly layer you can check out current snow coverage, even if you are miles away from the area.
The Sentinel Weekly layer also has options for false color visualizations. False color green is particularly useful for distinguishing between snow and bare ground. Furthermore, stacking Sentinel imagery with relief shading and/ or a topographic map like MapBuilder Topo allows you to figure out exactly what peak or slope you are viewing.
Displaying Sentinel imagery as false color green helps make the snow pop and stacking it with a topo map helps you to figure out exactly what features are snow covered- looks like the Silver Couloir is still holding snow in this example!
In addition to snow coverage, snow depth and quality are also important considerations for planning winter travel. Available to pro accounts or higher, the weather stations overlay allows you to display real time snowpack data, such as snow depth and snow water equivalent (SWE), from both SNOTEL and non-SNOTEL sensors in the area. You can view the current sensor readings or go deeper and display an interactive 7-day sensor history to examine how the snow has changed over the past week at that location.
Checking out snowpack stations and sensors in the area is the best way to learn about snow depth and quality.
Now it’s your turn! Are there any layers we missed that you find particularly useful for learning about current and forecasted conditions in the winter? Question or comments? Leave them below.
Next week will be the last installment of the winter travel series. We’ll be covering using the mobile app in the backcountry. Until then, happy mapping!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-01-12 14:42:082023-01-24 13:47:30Winter Travel Series #4: Learning About Current and Forecasted Conditions
This is the final post in a 5-part series covering our favorite CalTopo layers and tools for planning winter backcountry travel. If you haven’t checked out the other posts in the series yet, you can access them all here.
Using the Mobile App in the Backcountry
So you’ve done the work. You learned about the terrain using different base layers, added map objects to identify potential travel routes and areas of interest, evaluated your plan using tools like terrain stats and travel time, and narrowed down your options based on the current and forecasted conditions. Now it’s time to actually head out into the backcountry!
Now its time for the best part- the reason you do all the planning.
No matter where you are, the CalTopo mobile app makes it easy to access your map, update it as needed and navigate the terrain. Let’s explore how you can incorporate the CalTopo mobile app into winter travel.
Access your maps
With the CalTopo mobile app, there is no need to export your map data from CalTopo and then import it into another app or device. As long as you log in with the same account information that you used on the web, you will see all of your saved maps (including any maps created by other users that you’ve bookmarked) in the Your Maps list on the mobile app. This makes it practically seamless to plan at home and then access those maps on your mobile device for use in the backcountry.
Whether you create or bookmark a map on a computer or mobile device, the mobile app allows you to bring all the maps saved to your account with you.
However as you prepare to head out the door, keep in mind that you do need to have a data connection (either WiFi or cell service) to sync your mobile map list with the server. This ensures that your map list is up to date and you have the latest version of your maps.
Go offline
Many of the areas you travel to in the backcountry don’t have cell service (and for some people, that’s the best part!). If you have a mobile subscription or higher, you can download base layers and overlays, such as MapBuilder Topo or aerial imagery, to your mobile device. This allows you to use the mobile app offline in the backcountry. As long as you have layers downloaded, you can view map objects on top of those layers and zoom and pan around the map as you normally would, without a data connection.
Downloading layers such as MapBuilder Topo to your device allows you to use the mobile app offline. Looks like you’re ready to get offline!
This also allows you to put your mobile device into airplane mode while in the backcountry, which can help extend your battery life by preventing your device from searching for a cell tower. Conserving battery life is particularly important in the winter since cold temperatures can also quickly drain your battery. The other major contributor to battery drain? Excessive screen time. As much as we all want to know “How much further?”, being thoughtful and strategic about when you reference and use the mobile app is another way that you can further extend your battery life in the backcountry.
Record your track
As you leave the trailhead, recording your GPX track is a great way to track your location and create a record of where you traveled. It can also be helpful for ground truthing your original plan- did you end up traveling the route the way that you planned or did you make a detour? How long did it end up taking you?
With the CalTopo mobile app, you can record a GPX track directly on your map. This allows you to compare your planned route to the path you actually traveled. It also displays information about your elapsed distance, elevation and time as you travel the route, which can give you a good idea of how far you’ve come and how far you still need to go.
As you record your track, you view where you are on the map, where you’ve traveled and ongoing track statistics.
As long as you save the track directly to a map, it will become a line object on that map once you finish the track. You can add notes about how the actual route went in the comments for the line. Whether it turned out to be the pleasant option you expected or a brutal trek that you’re hoping to never repeat again, your recorded GPX track and any accompanying notes can serve as a useful reference if you head out in the same area again in the future.
Update your map
No matter how thorough your planning is, actually heading out into the backcountry will give you a lot of valuable information on your intended route and the terrain. Another advantage of using the CalTopo mobile app is that you can update your map as you travel the route. Adding and editing markers, lines, and polygons allows you to record valuable information to your map that reflects what you are seeing on the ground (if you click the links above, make sure to scroll down to see how to add map objects on the mobile app).
Find a good viewpoint? Add a maker so you can return to that location in the future!
If you have a data connection, these changes will be automatically synced to the server. If you don’t have a data connection, any changes will save locally to your device and then automatically sync once a data connection is re-established without any action needed from you. This allows you to continually update and refine your map.
Navigate in the field
While it is important to never rely solely on one navigation tool, the CalTopo mobile app can be invaluable for negotiating the terrain. You can use your mobile device’s GPS to display your current location on the map, alongside all your other mapping information. And as long as your device has an internal compass, the cardinal direction that the top of the device is facing will be indicated by a blue arrow and numerical heading, allowing you to translate your surroundings to the map.
Whether or not you are recording a track, you can easily locate yourself on the map using your device’s internal GPS and compass.
Trying to identify something that is further away from you, such as a peak? Turning on the heading line can be really helpful for identifying those types of features on the map, especially if the feature is pretty far off in the distance.
The heading line can help you hone in on exactly which peak you are eyeing in the distance. Oh hello there, Uneva Peak!
It is important to note that the CalTopo mobile app always has north up on the map no matter what direction you are facing. This type of map orientation is referred to as north up. The blue compass arrow (or heading line) will move to indicate the cardinal direction that the top of the phone is facing. If you aren’t used to it, it can take a little bit of practice to get comfortable; however one major advantage of using north up map orientation for winter travel is that you always know what aspect you are viewing.
Are there any layers or tools on the mobile app that you find particularly useful for planning winter travel that you think we missed? Tips or tricks? Questions or comments? Leave them below!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Meghanhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngMeghan2023-01-11 13:28:562023-01-24 13:48:08Winter Travel Series #5: Using the Mobile App in the Backcountry
We’ve just released a major UI overhaul for the desktop and mobile websites. We had two major goals with this project: first, reduce the variation between the desktop web, mobile web, and app UIs. And second, address some recurring issues around discoverability and ease of use.
The UI is now better grouped by functional area. We’ve moved your account data into the top bar, so that the left bar is dedicated to map objects, and most mapping related functions are on the map itself. We’ve also replaced the mouseover menus. An more in depth overview of the new UI with comparisons to the previous UI is found here.
Other major changes include:
Keyboard shortcuts for commonly-used tasks
Clicking on the map brings up info for all nearby objects – no more struggling to click on exactly the right spot
We now have separate “Log In” and “Sign Up” actions to help people catch when they accidentally login with a new account provider
Rendering object labels with halos instead of large white blocks, to improve label visibility on complex maps
On the left side of the map the map objects list is now solely focused on map objects including importing, exporting, and adding new objects. When minimized, the add button moves onto the map so you have more room to work!
Tasks such as printing, measuring, saving, and sharing maps have moved onto the map and menus now are based on a click instead of mouseover.
The right side of the screen remains largely unchanged, with layers listed on the left, and the preset layers at the bottom on the left side. Note many layers now have keyboard shortcuts, you’ll see those listed next to the base layer you select on the right hand side (if the base layer has a shortcut), and next to a variety of overlays on the right as well.
One of the largest changes is that the top bar is now primarily focused on account level tasks such as log in, creating accounts, managing your account or team data, and managing your subscription.
As with any update there may be inadvertent errors or omissions. We’re always here for you at caltopo.com/help and over time we’ll update screenshots throughout our excellent user guide to reflect the new UI. Thanks for supporting CalTopo!
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Ben Lantowhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngBen Lantow2021-04-15 11:09:112021-05-24 13:35:06Dude, Where’s my UI?
Oftentimes, people write in asking about differences in our reported data on how long a particular hike should be versus how the distances they traveled were in their own experience on the trail. So I set out to gather data about why this could be.
First of all, let’s take a look at what GPS is and how it works. As you probably know, the Global Positioning System is a set of satellites that orbit the planet constantly, and send signals that work using trilateration to determine your location on the planet. The signal is not so important as the time that it takes for the signal to go from the satellite to your device. This time is what allows the processing software to determine your location.
Many backcountry travelers today use a GPS device of some sort – whether as a reference tool or, at the other end of the spectrum, as a full navigation and data collection tool. For many people these days, that device is their smartphone, which typically has a GPS receiver built-in. The quality and accuracy of that receiver varies widely depending on the device. The accuracy of the identified position depends on both the signal coming in from the satellites, and on the device receiving those signals.
According to www.gps.gov, the website of the US government GPS program,
The accuracy commitments do not apply to GPS devices, but rather to the signals transmitted in space. For example, the government commits to broadcasting the GPS signal in space with a global average user range error (URE) of ≤7.8 m (25.6 ft.), with 95% probability. Actual performance exceeds the specification. On May 11, 2016, the global average URE was ≤0.715 m (2.3 ft.), 95% of the time.
So the signal coming from the satellite is one part of the accuracy equation, but not the full value that becomes user accuracy. Many factors influence the user accuracy, such as satellite geometry, signal blockage or reflection, weather and climate conditions, and the actual receiver design and quality. For an incoming signal under ideal, perfect conditions, GPS enabled smartphones are typically accurate to 4.6m horizontal error.
While you may be thinking that 4.6 m horizontal error is not the utmost degree of perfection that you expect, I find this pretty amazing. My phone can identify my location anywhere on the earth to an accuracy of around 15 ft in a matter of seconds. That’s astounding!
Ah, but there’s another twist! We have to consider topography. GPS accuracy calculations are based on a full and open view of the sky. Without this, our accuracy can decline even further. Trees, rocks, canyons, mountains, buildings – all of these will have a huge impact on your signal. The number of satellites that your receiver can connect to has a strong effect on how accurate it calculates your location. It’s not uncommon for satellites to be pretty close to the horizon, with the result that you can only get a signal from 3-5 satellites when in the mountains. It takes a minimum of 4 to get your location and elevation.
So to test these theories out, I went on a nice long day hike. My planned route came out to 14.5 miles, using a combination of snap-to data via OSM, and some hand drawn off trail hiking by points (as opposed to freehand with shift+click). Between the two of us hiking together, we had 4 different devices.
The hike started in the trees and thick brush, near a steep mountain face and with the horizon high above us on all sides. After a few miles we topped out onto the cap and wandered in and out of trees, across granite slabs, along many lakes, over some talus, through thunderstorms and rain, back to sun, some wind, and finally dropped back down into an increasingly deeper valley with more and more vegetation.
Back at home, I imported all the raw tracks from the 4 devices into CalTopo and viewed them all together.
Here’s an example section of the raw data:
Android phone via CalTopo app: 18.01 mi, 3259 ft.
iPhone via Caltopo app: 18.63 mi, 3026 ft
Suunto Spartan: 16.42 mi, 3141 ft
Garmin Fenix: 17.30 mi, 4078 ft
Adjusted drawn route: 15.11mi, 3009 ft
Here is an example of the four tracks and the planned track (red?)
Scale of the above image is about 1700ft left to right, 1000 ft top to bottom.
As you can see, there is a lot of variability between the tracks. And these are from two people walking the trail at the same time, same day, same weather, same cloud cover, even the same app in two cases.
Tracing a well-referenced aerial or satellite image is considered to be an accurate-enough way to draw a trail and determine its length. When good satellite imagery is not available and/or tree cover, shadows, or other challenges make it hard to use these images, it is possible to create a line to represent the trail by using a track bundle – a collection of many tracks of the same route. Programmers can then create weighted averages of the routes, and publish those averaged routes as the trails. The more data used to calculate the line, the more accurate the trail map becomes.
Raw GPS data is messy, and so some programs use techniques to smooth the tracks when recording or importing them. Some apps, devices, or programs apply a smoothing algorithm to the track. These algorithms vary in how they function, but generally they calculate whether to keep any particular point based on the points around it and the speed at which the points are generally collected. These algorithms also might have a hard time distinguishing a snack break from a place where your location points bounced off a nearby cliff over and over. Smoothing can also be done by hand to match a track to a visual image, such as aerial photography that is georeferenced.
To try out my own hand at visual track smoothing, I took my Android track and set it over some satellite images and started editing points. I moved points where the recorded track jumps far off the trail that I hiked, lining the points up better with the route on the ground. I shifted whole sections of the line to be over the trail in places where it was significantly off the trail. I moved other individual points to make straighter lines where it made sense to, and removed points that were extraneous or clearly way too far off the route that I actually walked. There were also some areas where the track recorded a straight line where I assume that my phone lost the GPS signal for a bit, so I moved that track onto the actual trail as best I could. This changed the length of my track to make it about 1.27 mi shorter than recorded, from 18.01 mi to 16.74 mi.
For a couple sections of the trail I wanted to try to be even more accurate about comparing the recorded track to the actual trail. I chose an area where the trail was clearly visible in the satellite image, and located on a ridge top with widely spaced trees. In the image here, the raw GPS data measured 1,307 ft, while the actual trail traced to be 1010 ft. That’s a 23% difference. Given that number, I’m impressed that my whole trail is only off by 7% between the actual and smoothed track, and 13% or so off from what my pre-planned route was.
At this time, CalTopo does not do any line smoothing when recording tracks in its own app. All the error of the device and conditions remains present, and you may see wildly different distances recorded vs what you expected from planning your trip by drawing lines. As we have discussed, these errors in track length are expected and part of the experience of using GPS products.
GPS Elevation
GPS receivers need signals from a minimum of four satellites so they can calculate elevation. However, reported elevation has even more variability and inaccuracy than horizontal location does. Many apps and programs therefore do not rely upon GPS elevation data. Instead, they refer to a Digital Elevation Model (DEM) for much more accurate elevation readings at any given point. Therefore, when a line or other object is plotted onto the coordinate grid, the DEM can look up the elevation at that location, ignoring any elevation submitted from the satellite signal calculation.
Some more expensive GPS devices come with a barometric pressure sensor that can calculate elevation in real time, without the satellites. The user then has the choice to use the baro pressure or a DEM lookup to set the elevation after recording the track.
Improving Accuracy in GPS
One way that devices can improve accuracy is by using additional frequencies sent from the GPS, as well as the phasing of the signal from the satellite. High end commercial survey devices can gather a much more accurate point. Also, by taking many points over time in the same location, surveyors can gather more accurate information, using a scatter plot technique. As a result, high end devices can determine a location down to centimeters, or even millimeters if many points are collected.
The US government is in the middle of a decade-long process to update the accuracy of the GPS system, adding several new civilian signals. In the past, some civilian GPS devices have taken advantage of the L2 frequency, though it is encrypted for military use. Because the GPS unit can still see the signal (though it can’t decipher it), it can use the timing of this signal compared to the L1 signal to calculate a more accurate position. As new signals come online with additional satellites launched carrying upgraded equipment, civilian GPS accuracy will improve over the coming years, though these signals also require upgraded devices on the receiving end.
Some GPS receivers can also pair with the FAA Wide Area Augmentation System (WAAS) that can help perform differential correction of location in “real time” Survey grade devices using combinations of technologies can get data under 1m accuracy.
Some newer GPS receiving devices can now also access GLONASS and Gallileo, which allows access to all of the three major GPS satellite systems worldwide – the US, the European, and the Russian. By combining these systems and accessing a much larger network of satellites, units capable of connecting to multiple sources can achieve a much higher level of accuracy of position.
So the type of device you have for receiving the signal matters in a large way. As we saw in the example earlier, where you are using the device matters with tree cover, cliffs, or large buildings affecting how well the GPS signal reaches the device. Additionally, atmospheric conditions and the satellite positions at the time of the data acquisition will affect accuracy.
Conclusion/ Understanding your location
Why even bother using GPS if it’s so bad? You might need to just let go of your feelings about how specific your location or map needs to be in order to accomplish your goal. Unless you are a geologist measuring compression of the rock above the Cascadia Fault, millimeters, or even up to meters of precision are just not that helpful for your 7 mile hike. These days we have very accurate measurements of summits of mountains, road alignments, and elevation profiles in some areas. If you are standing on a peak that the map says is 12,348 feet but your GPS says 12,326 feet, you should probably trust your senses that you are in fact on top of the peak, with the USGS survey marker under your feet. By the same token, if you are on the summit and reporting your coordinate position over a radio, you should have some idea of how many digits are relevant. If your device is telling you it knows your location to ten decimal places, it is not acknowledging significant figures somewhere in it’s calculation of your location, and thus is making the fool of you.
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Ben Lantowhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngBen Lantow2020-10-12 11:22:472021-05-24 13:34:31Maps and Tracks: Accuracy, Precision, and your Phone GPS (Part 2)
We are frequently asked about our maps, their accuracy, and the accuracy of tracks, routes, and lines. This is part one of a two part series to help explain some of the nuance in mapping. Inherently this can be a bit of a dense topic so we’ve broken it down with some clear sub topics that may be of interest.
Is CalTopo’s map wrong? Of course it is! All maps are inherently wrong to some degree. There are many ways to evaluate how “good” a map is, and all of those evaluations are subjective based on the needs of the map user.
Maps are by nature inaccurate to some degree. Maps represent the real world at a given time and place. The real world can change over time with dramatic events such as landslides, or something as little as a trail re-route. Each place is interpreted by both the map maker and the map user. The map maker chooses what information to include in the map, where to source that data and how to display the results. The map user interprets the map based on what they are trying to use it to accomplish. A hiker may use the same map very differently than a paraglider.
We build our maps from other sources. CalTopo does not go out in the field and measure things or inquire about the name of a feature. Our goal is to provide you with lots of options, and build a program that allows you to add your own information to a map, or use the existing base maps to navigate or discover things.
GPS on your phone is not as good as you might imagine it to be. It’s actually really good when you consider all the technology in place to allow your phone to find your location anywhere on the earth in a matter of moments. However, if you are looking for really precise information about how far you just hiked down to the foot, or even to the quarter mile, that’s just not a thing given the conditions where most people hike.
Below we discuss the details of all these principles extensively. If your interest in the specifics of map making and GPS accuracy is piqued, read on.
What Makes a Map?
To begin to address the question of how good is a map, we need to consider some basic principles of cartography, the science of map making, and Geographic Information Systems (GIS). Here is some background information to get you started:
Principles of Measurement: In regards to measurements, what is accuracy, and what is precision? While related and sometimes dependent on each other, these two properties of a set of measurements are not the same thing. You can think of an accurate measurement as one that is very close to the TRUE value of the thing being measured. For example, a GPS signal from a satellite may be said to be within a 4m accuracy 95% of the time. A precise measurement is one that is consistent with other measurements of the same phenomenon. If the values given consistently fall close to each other, then the set of measurements is precise. If your GPS unit consistently puts you 4-5m west of the summit of a peak while you are standing on the peak, it may have a very precise measurement, though it has a systematic accuracy error.
The Shape of the Earth: The earth is neither round, nor perfect elliptical. Presenting a round surface via a flat surface is mathematically impossible, and doing so for something that isn’t even perfectly round is even more difficult.
The Map is not the Earth: Just as the architectural drawings are not the building, a map of a forest is neither the forest nor the trees. The goal of a map is to represent something that we otherwise can’t fully see or understand without using a reference tool. The map is that tool. The map intentionally distorts reality to make it easier to understand, reference, and use.
Map Scale: Maps are produced at scale to represent locations on the surface of the earth. Scale is directly proportional to the accuracy of any point on that map. Small scale maps show relationships between distant and large objects but would have a hard time designating small, detailed objects. Conversely, a large scale map shows a smaller geographical area and is more accurate in regards to smaller objects. Large scale maps are represented by smaller numbers on the right side of the ratio expressing the size (IE 1:250,000 is a small scale covering a wide area, while 1:12,500 is a large scale covering a small area.)
Map Purpose: The purpose or intended use of the map matters with regards to the needed level of accuracy. There is little practicality in making a map intended for hiking to be accurate down to the centimeter. While we might want to know the exact height of a mountain down to the centimeter in order to find out which is the tallest, the length of a trail measured to this detail would be impractical and not very useful. If a hiker walks the inside of every curve and another hiker hikes the outside of every curve, they would walk different distances, but not in a way that would appreciably matter.
Every map aims to show something different to the user, and much of this depends on the purpose the map maker had in mind for the map. Sometimes they may be more aesthetic than practical, and other times so exact about one thing that they miss an opportunity to share other important information. At CalTopo, we offer a collection of maps that we refer to as base layers. Each map we offer in the base layer and overlay lists has been carefully selected to provide data that
Is meaningfully different from other layers already provided,
Is useful to users in the world of outdoor pursuits, disaster response and search and rescue, and general interest, and
Provides accurate and quality information.
Basic Map Types
Maps generally fall into one of two categories: reference maps and thematic maps. While thematic maps often look to answer a single question or concept, reference maps aim to provide an array of information that allows the user to identify objects, relative locations, distances, areas, finding a route, or understanding topography and vegetations – all in one map. The base layers you find in CalTopo are generally reference maps, as they contain a variety of information and topography. Overlays are more similar to thematic maps. For example, the max wind speed overlay shows no information other than a plot of the predicted wind speed. It doesn’t reference natural features, roads, or vegetation. It covers one topic only, though that topic is tied to locations on the surface of the earth.
Reference maps are often used as base maps for adding additional geographically referenced features on top of those maps. Reference maps are built using a variety of tools, and many of those tools have become more and more powerful over recent years. Satellite and aerial imagery play an important role in building maps, and increasingly tools such as light detection and ranging (LIDAR) bring high-resolution elevation data into the mix. This data allows more accurate slope angle analysis, elevation calculations along a line, and small-scale changes in elevation.
Within CalTopo, some layers are dynamic and incorporate new data as it becomes available (think living, breathing layers) whereas other layers, such as the Scanned 7.5′ maps, are digital images of maps designed at a particular point in time, many before Geographic Information Systems (GIS) even existed.
Raster Vs Vector
Digital maps come in two forms: raster and vector. Raster data are grids with values set per grid cell. Elevation data is typically stored and displayed in a raster format. It is continuously variable, starting from some set value such as mean sea level, with each cell falling a specific distance above or below that established zero level. However, raster data is not always visually pleasing and can be more difficult to interpret. For example, the Fire Activity overlay in CalTopo is raster data. Each star and circle combination represents one cell of data. Each point represents a positive indication of a hotspot within the raster cell, and the circle represents the error radius of that data point. The larger circles mean that the angle of view from the satellite is more oblique than from straight above, and so the error radius for the where the hotspot is located is larger.
Vector data is composed of points, lines, and polygons and can grow and shrink with scale. The main advantage of vector data is that visually it is more pleasing and natural to understand. It works well for representing objects that have discrete boundaries, such as roads or coastlines. Processing vector data can be challenging and memory intensive.
Maps generally fall into two categories, reference and thematic, and are made of two types of data, raster and vector. These components come together to build the map, along with the goals of the map maker and target users, and the cost of obtaining and assembling data. Each map therefore has a practical limit to its level of accuracy. The next section considers map accuracy more closely.
Building Accurate Maps
Let’s play with a thought experiment. You are building a new map from scratch and you go out and climb two peaks and measure the distance between the summits of those two peaks. How accurate is the distance you measure? More importantly, how accurate does it need to be? Say each peak has a pile of rocks on top, and during winter snows, the top most rock shifts a few centimeters to settle a little more into the rocks around it. Is your measurement now wrong? How much does it matter, and to whom? Would those few centimeters difference make it significantly easier to get to the top of the peak? Probably not. Now consider that to build your map, you need to measure 5 peaks, or 10, or 30, and their relationship to all the other peaks around each. The practicality of measuring each of these down to centimeters is pretty low considering that the scale of your map is going to be something like 1:12500 and there is no way to represent those centimeters of difference on your map. Adding labels to your map to show these very exact differences would obliterate the ability to see anything else. It would no longer be a reference map, but a thematic map conveying only one small subset of information, and not very useful for navigating. In fact, for the purposes of navigating across terrain, even being a meter or so off in any direction really doesn’t matter that much. In fact, the USGS only guarantees 90% of well-defined points to be accurate to within .02 inches of their actual positions on maps with a scale smaller than 1:20,000. On a map with a scale of 1:250,000, this translates to an accepted error of over 400 ft horizontally.
Maps are inherently inaccurate. They are always a representation of the real world, and not the real world itself. This is the philosophy of mapping at its core. Every map maker must decide what information to include on the map, based on what the purpose of that map is and who will be using it. No map can include everything that any person may want to understand.
One way to improve map accuracy is to gather data from many, many sources. An open-sourced mapping project called OpenStreetMap works with contributors worldwide to gather and maintain geographic information for building maps. Anyone can create an account and start contributing to the project. The more users that add GPS traces or that draw over satellite imagery for a particular location, the more accurate that feature becomes over time. In areas with a lot of users and traffic, OSM data can be highly accurate. CalTopo draws from this data for a significant portion of the map products that it builds. We offer the MapBuilder Features overlay to add information about the route designations included on the map.
CalTopo does not go out into the real world and measure things on the ground and build maps from that data. We use a variety of well-established data sets and sources to assemble the layers you see as options in CalTopo. Some of these are fully produced layers and we pull the tiles in to display via our system. Others, like MapBuilder Topo and Custom MapBuilder layers, are groups of data such as land cover, slope angle, elevation, and roads and trails that can be assembled to create a map.
Using Layers to Better Understand Terrain
One person’s idea of a trail may not match another’s idea of the same trail. Let’s look at an example of how OSM data and USFS data show different details about some trails. Consider a “social* trail” or a “climbers trail”. These may show up on maps as trails, but on the ground they are faint, difficult to follow, unmaintained, overgrown, or involve scrambling over small cliffs. They may still be important to have on the map: the climber may really need a reference of the safest route to descend from a climb. The hiker may find that same trail to be extremely dangerous. Thus, the user must consult various maps and any associated reference materials to understand what the intended use of the map is and what routes are represented there.
Sometimes social trails are not approved by the land owner or manager. Just because someone mapped it doesn’t mean that it’s a legal trail. It’s always your responsibility to understand the land use rules in a given area. A map may have the trail on it because the map maker views the map as a documentation of what exists on the ground, rather than what the approved travel routes are.
One quick and helpful way to find out how useful a particular map base is to your goal or project is to compare it to other maps of the same location. This is the principle behind offering many Base Layers in CalTopo. Each of our base layers is carefully selected to complement and contrast other base layers, in order to provide a breadth of different information.
The two images below represent the same location. The first is from the MabBuilder Topo base layer, and the second is the FS 2016 base layer. The prominent red trail across the center of the first image is missing in the second layer. If you look closely, you can see the black portion of both trails in each image. Why is the trail missing on the USFS map – an official map for the Forest Service?
IMG 1
IMG 2
Turning on the public lands overlay, I can confirm that the trail is on USFS lands, so it’s not an issue of the USFS maps sometimes covering areas that aren’t USFS land. Turning on MapBuilder Overlay, the trail returns to the map. Thus we can assume that the trail is in OSM data but not in USFS data.
A probable explanation for this difference between the base layers is that the trail we see in MapBuilder is not an official and maintained trail. It may have been a trail in the past, and now is used by backcountry explorers and people climbing peaks in the area. A hiker that isn’t used to following faint and broken trails may have difficulty on this route, while other backcountry travelers may find this trail to be more fun than other, clearly marked ones. At other times, a trail that appears on one map but not another could be illegal, closed, rerouted, or rehabilitated. So, this is a great example of how using a variety of base layers and map sources can help you plan. (You can also refer to the MapBuilder Features overlay to learn more about a specific path and determine the quality of trail it is categorized as.)
https://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.png00Ben Lantowhttps://blog.caltopo.com/wp-content/uploads/2019/10/caltopoLogo_menu1.pngBen Lantow2020-10-08 13:15:302021-05-24 13:34:46Maps and Tracks: Accuracy, Precision, and your Phone GPS (Part 1)
Note: This post was updated on 9/11/20 to include information about the GOES Live Fire Layer as well as the GOES Live Satellite Imagery. We also attempted to address some of the most frequent questions we’ve gotten over the last few weeks in our help forums.
With the increase in wildfires across the Western US in the last week we’ve seen a huge spike in usage on CalTopo as well as numerous questions. This post contains a LOT of information about imaging, data sources, and methods, some of which was previously covered in some older blog posts in 2017 and 2018 but is updated here.
First and foremost: If you’re in an area near a wildfire follow your local authorities for evacuation notices and up-to-the-minute information. If you are in a life-threatening situation CALL 911. While maps provide valuable insights into fire behavior and areas affected, a map is always just a representation of the best available data. Sometimes data is delayed or erroneous. Above all things, please stay safe and healthy.
Data Sources
CalTopo aggregates data from a large number of sources that provide insights for fire fighters, fire managers, and the general public. These features have been added over the years, unfortunately usually as a result of fire activity. One of the informative and currently relevant is the Fire Activity overlay.
The MODIS program consists of two satellites Aqua and Terra, that pass around the Earth covering the entire Earth once every 24hrs. As of 8/16/20 the Aqua satellite is not producing fire data consistently (reference here). MODIS satellites have a resolution of 1km, which means that they can differentiate down to a 1km square but within that km x km box the satellite cannot further differentiate where heat/smoke are. MODIS data is available as a standalone imagery layer (Daily or Nightly Low-Res in the base layer drop down).
VIIRS
The VIIRS program is a newer program and provides a higher resolution than MODIS (375m instead of 1km, more than two times better). VIIRS similarly provides multiple passes around the Earth every 24hrs with two different satellites and is a major part of the current fire activity layer. As with MODIS, VIIRS images from the NPP satellite are available as raw images. However unlike MODIS, in the fire activity layer both VIIRS Satellites (NPP and JPS-1) are labeled VIIRS on the map.
NIFC
When selected the current fire activity layer displays satellite data in conjunction with data from the National Interagency Fire Center on the map. NIFC maintains data from incident managers including specific incident mapping obtained using GPS tracks from group crews and information from firefighting aircraft.
NOAA Hazard Mapping
NOAA Hazard Mapping provides 3 levels of smoke polygons, from low to high smoke (lightest grey to black in the images). The data is displayed only when “with smoke” is selected. The polygons can be very large and overlap with a lot of other data. This provides some insight into smoke, although it doesn’t tell us how bad the air quality or smoke is in that path. We’re continuing to look at adding air quality information and other smoke forecast information in the future.
Note that a satellite has to pick up the hot spot, the image needs to be processed and then the data has to be pushed out publicly for a fire to appear on our maps. With the recent lightning fires in California and with the incredibly dry conditions, fires started quickly and spread very rapidly. We saw delays of 12+ hours after starting before fires would appear in mapping. Fires can start very rapidly and grow incredibly quickly and VIIRS and MODIS programs only pass over the Earth 1-2 times each day.
Using the Fire Activity Overlay
There is a drop down menu for the Current Fire Activity overlay that allows selection from All Satellites, with smoke, MODIS, VIIRS 375m, VIIRS Progression, and IR Progression. Each option provides a slightly different dataset or view. As you zoom in on maps additional information is revealed.
All Satellites, MODIS, VIIRS 375m
The infrared data from both MODIS and VIIRS contribute to hotspot detection, from which we can infer fire activity. As seen above (this image is from the 2020 LNU Lightning Complex Fire) the time and date of each hot spot along with the satellite that the data came from is always available. If you select just MODIS or VIIRS 375m from the dropdown menu you’re also able to see temperature and power (measured in megawatts) of that data point. This is shown below.
Each hot spot also has an error radius around the point based upon error reporting from the satellites. The location of the satellite in relation to the Earth, as well as the resolution of the instruments on the satellites feeds these error rings. The best view of the Earth from a satellite is from directly above, toward the edge of images the view becomes more oblique and can result in more error (MODIS satellites are especially prone to this), this would be represented by larger circles around hot spots. A good option may be to switch satellites to get a better vantage point. Additionally we see some “false positives” along or ahead of the edge of the fire, while the reasons for this are not exactly clear, it likely has to do with the satellites sensing heat from smoke and gases coming off the fire. Finally each hot spot is color coded based on time of the report. Red are most recent (less than 12 hours), then orange (12-24 hours), and finally yellow (24-48 hours). After 48 hours we remove the hot spot from the map.
Additionally we display the active fire perimeter from the National Interagency Fire Center (formerly GeoMAC) on all the satellite views. These perimeters are updated 1-2 times daily typically and come directly from incident management teams. They are based on a combination of reports from fire crews, satellite information and fire aircraft doing infrared flights or firefighting. If the fire has been named that name is also displayed on the perimeter polygon. This is shown below with the perimeters for the Loyalton Fire in Northern California (below left). When zoomed further out these perimeters become a small flame icon instead (Northern California/Nevada in August 2020 is shown below right)
With Smoke
The “with smoke” option adds the NOAA Hazard Mapping System smoke data. The smoke is designated with gray to black crosshatched polygons, the lighter the polygon the lighter the smoke (light gray is low, grey is medium, black is high). (Smoke over California and Nevada in August 2020 are shown below).
VIIRS Progression and IR Progression
The other options in the dropdown are progression layers that show a color coded progression over longer periods of time. The VIIRS progression layer shows VIIRS hotspots for more than just the 48hrs the baser layer does (a legend is under Fire Info in the top right of the page). The IR Progression layer is currently disabled due to changes in the way data was reported, we plan to update and bring it back online in the coming months.
GOES Live Fire Detection (Experimental)
GOES 16 and 17 are geostationary satellites positioned over the eastern US (16) and western US (17), streaming images back to Earth on a near-real-time basis (within 10 minutes, as compared to the above discussed VIIRS and MODIS satellites). The imagery from these satellites is frequently used for animated loops of hurricanes and other large-scale weather events. In addition to raw multi-spectral imagery, NOAA also releases a number of derived datasets, one of which is active fire detections. In the daytime, these fire detections are reported at 5 minute intervals.
CalTopo has incorporated the active fire detection information on our maps, seen right. The layer is found right below the Fire Activity Layer checkbox and is called “GOES Live Fire Detection”. The colors of pixels correspond to the time of the fire detection, the legend is available the top right corner and there is no information about temperature available in this layer, Active Fire Overlay provides that information.
This layer is updated live (new information within 10minutes at the longest). In addition to the satellite’s rapid update interval, the CalTopo map layer will auto-refresh to ensure you are always looking at the most current information, and the time of the last satellite image is displayed on the layer. For new or rapidly moving fires, this can be useful information to supplement between MODIS and VIIRS satellites passes from the “fire activity” layer.
However, each pixel is roughly 2km by 2km, so this layer will only show larger fire activity. An error of a single pixel is enough to place a fire over a mile off from its true location – this is not a layer that will give you insight down to the level of whether a specific neighborhood has burned. The “fire activity” layer is better for that use case, although even that is still an imprecise tool that only reports approximate locations and is easy to over-interpret as having more precision than it does.
Using Other Overlays for Fire Information
There are a number of other live data overlays available in CalTopo that can help inform fire behaviors. Both live temperature and wind layers can be useful and are found listed under Weather Forecast. Both are based on live NOAA data. The wind plot shows current wind direction (indicated by arrows) and speed (indicated by color with a legend on the page in the top right corner). There are dropdown menus to select speed versus gust speed and for time (from now all the way out to 36 hour forecast speeds). We also maintain a fire history layer with about 20 years of fire history also from the National Interagency Fire Center (image far right). While this isn’t much “history” it’s the best source of data we’ve found to date. Perimeters are colored by age, with name and year the fire occurred listed as you zoom in (here, red again is most recent)
CalTopo has also incorporated the. realtime imagery from GOES 16 and 17 which can be found as a base layer called GOES Live (seen right). The realtime imagery is kept up to date and automatically refreshes just like the Realtime fire layer. Images will be delayed no more than 10minutes from time of acquisition and typically smoke is visible from this layer, as are other large scale meteorological events (such as hurricanes, storms, etc).
Because the GOES satellites are geostationary and far from the Earth resolution of this layer is limited (around 1000m resolution), you won’t be able to see your house or van from the images. The Global Satellite Imagery layer, NAIP Aerial Imagery, or the Google Maps Satellite layers all provide much higher resolution (as high as 0.5m in places, though mostly between 1-5m resolution) , however they are only updated every few years, not in minutes. The Sentinel Weekly imagery is a happy medium providing a high resolution layer updated every 5 days that displays approximately 10m resolution images that can be used for things like snowpack detection as well as some evaluation after fires. Sentinal imagery requires a Pro subscription to use.
Other Data Sources
There are a variety of other data sources to inform decision making about fires. Local sheriffs’ offices, fire departments, and emergency management agencies provide a huge amount of information about fires nearby, and are proactive with pre-evacuation notices and evacuation notices. Additionally inciweb is a huge source of information with contact numbers, resources, fire size, containment, and evacuations. NIFC provides more general wildfire information and has links back to inciweb for further details about specific fires.
For a couple sections of the trail I wanted to try to be even more accurate about comparing the recorded track to the actual trail. I chose an area where the trail was clearly visible in the satellite image, and located on a ridge top with widely spaced trees. In the image here, the raw GPS data measured 1,307 ft, while the actual trail traced to be 1010 ft. That’s a 23% difference. Given that number, I’m impressed that my whole trail is only off by 7% between the actual and smoothed track, and 13% or so off from what my pre-planned route was.
