New Year, New Layers

In my last blog post, I mentioned that I spent the tail end of 2016 cooking up some new map layers.  Well, here we go.

Terrain Shading and Custom Relief

In SAR, it’s not uncommon to have a group of people huddled around a large-format map, looking at it from all angles.  While relief shading helps terrain features pop, it only works when the map is viewed from the bottom – standing at the top will cause features to invert with peaks looking like valleys.

One alternative is terrain shading (for lack of a better word), where the relief is generated using a number of different light sources, rather a single 315 degree (NW) angle.  Because of the multiple angles used, there is no “up” or “down”, and the map can be viewed from any angle without playing tricks on the eye.  The downside is that in some areas it can be hard for the eye to quickly tell up from down.

For CalTopo’s terrain shading, I tried to balance these tradeoffs by using 6 evenly spaced light sources plus an additional one at 315 degrees, proving a slight amount of orientation.

CalTopo enhanced relief, which uses a multiply blend filter but retains the standard 315 degree light source

CalTopo terrain relief, which uses a 7 different light sources

If the out-of-the-box terrain shading doesn’t quite work for you, there’s now an “Add Custom Relief” option under the Add New Layer menu.  Pick an azimuth (compass direction) and zenith (angle above the horizon) and click “Add Lighting”.  Mix and match multiple combinations to reach your desired effect.

FSTopo 2016

The FSTopo maps behind the “US Forest Service” map layer have been seeing regular updates, but it’s not all forward progress.  While the newer maps gained vegetation shading and better road/trail data, the delineation between public and private property moved from light, transparent gray shading to a heavy-handed gray that completely obscured all vegetation shading.  I wasn’t happy with the way this looked, and wasn’t happy dropping public/private land boundaries, so I did things the CalTopo way: create a new layer.  And thus the USFS 2016 layer was born.

For most purposes the now-renamed “FSTopo (2013)” and “FSTopo (2016)” layers will be interchangeable.  The old layer is better for locating land boundaries, and its white background works well for blending with aerial imagery or slope angle shading.  With its vegetation shading, the new layer is probably better suited for standalone use.

The same map as above, but this time using the “FSTopo (2016)” layer.

Expanded Alaska DEM Coverage

While not a new layer per se, I’ve been slowly expanding CalTopo’s Alaska coverage.  Although the national elevation dataset (NED) still only covers a portion of the state, that portion has been growing, and it’s time to catch up.  The NED isn’t a first-class layer, but a powers a lot of other ones, including normal relief, enhanced relief, 40′ contours, fixed and gradient slope angle shading, custom DEM shading, and cursor point elevations.

The current state of NED-based layer coverage in Alaska.

Note: I’m still patching up a few small errors in the dataset, but didn’t want to hold this announcement up until those were fixed.

New NAIP Imagery Layer

The new layers based on the National Agriculture Imagery Program (NAIP) dataset are probably worthy of a blog post all their own.  But before I get into the good stuff, know that all this layer creation doesn’t come cheap, and high quality imagery is definitely the worst offender.  Not that I’m complaining or looking for your sympathy, but lest there be any doubt as to whether your subscription dollars are getting rolled back into CalTopo development:

By way of background, while Google’s Satellite layer is great, I can’t do any server-side manipulation on it, whether that’s generating PDFs or combining it with enhanced relief shading.  Although a secondary issue, I also can’t provide offline copies of it for use by SAR teams in remote environments.

NAIP data has always been public, but in the past, acquiring it was a bit awkward, requiring the mailing of many terabytes of drives back and forth.  I tried to skirt around this by stitching the aerial backgrounds from the USGS’s new “USTopo” maps into a seamless layer called USTopo Imagery.  This worked, but the quality wasn’t great, and update cycles were delayed vs going directly to the source.  I’ve been on the hunt for some time, and as drive costs dropped, was seriously considering biting the bullet and acquiring a physical copy.

Then Andrew Johnson from Gaia GPS pointed me at the aws-naip public S3 bucket, and it was off the races.  Yes, this was expensive.  Yes, it’s a roll of the dice when big-name companies like Google, MapBox and ESRI have better datasets out there.  From a business perspective, maybe it won’t work out.  But I believe that high quality aerial imagery that I can repurpose as needed is strategically vital to CalTopo’s future, so I decided to roll the dice and here we are.

The biggest difference between the NAIP and USTopo Imagery layers is quality.  The NAIP layer goes to zoom 17 (~1m per pixel) while USTopo Imagery went to 16 (~2m per pixel), but even at zoom 16 there’s a noticeable quality difference between the two.

USTopo Imagery view of “Half Dome Village” aka Curry Village, Yosemite NP

Same location viewed using the NAIP layer

NAIP is generated in 3 year cycles, i.e. one third of the continental US is overflown each year.  Not content with a single NAIP layer, I generated two versions – one for 2011 to 2013 and one for 2013-2015.  Most places in the continental US should have two different dates available, either so that you can see how things have changed with time, or in case one revision has too much snow, shadows in the wrong place, etc.  Long term, I hope to grow the date range.

Prior imagery of the same location.  In this case, it’s not much different.

NAIP is also distributed as 4-band imagery, with a near infrared channel in addition to the standard red, green and blue.  I captured this and rendered it out into a separate layer, which allows for some interesting data processing.  Right now, I’m still conflicted as to whether it’s actually useful or just a neat party trick.

The Aerial Imagery section of the layer dropdown now has a “False Color IR” option.  This uses the near IR channel for red, red for blue, blue for green, and drops the green entirely.  As a result, the difference between near IR and IR is accentuated, drawing stark contrast between vegetation and manmade, dirt or rock surfaces, regardless of actual color.

False-color IR view.  No, it’s not some weird 3D glasses thing.

The computed difference between red and near IR is also available as a vegetation shading option for custom MapBuilder layers, called “Infrared Reflectance”.  With this option you can generate traditional looking topo maps with super-accurate vegetation shading, but as always there’s a catch: areas that were shadowed in the original image show as white rather than the appropriate vegetation shading.

Custom MapBuilder layer with the IR Reflectance background.  Note the white band in the meadow at the top of the picture, which is shaded in the original image, not actually vegetation-free.

Deprecation of Existing Layers

With the layer dropdown getting increasingly complicated, this was also a good time to clean house.  The “ArcGIS Topo” option isn’t as clean as my USGS map scans, but I originally included it because it covered Alaska.  That’s no longer an issue, so it’s gone.  USGS 1:250k maps aren of limited utility with Google Terrain and MapBuilder Topo; gone.  USTopo Imagery is inferior to the NAIP layer in pretty much every way; gone.  CA Visitor Maps had some visitor maps that can’t be found elsewhere, but I need to move past state-specific layers in the dropdown, and I hope to grow the NPS and USFS visitor maps soon to help make up the gap.

All of these layers are still accessible in two ways.  First, any existing maps or links that referenced them will continue to work, although they won’t display properly in the layer dropdown.  Second, they’re all available as prefill custom sources.  Click on Add New Layer -> Add Custom Source, and choose the layer you want out of the “prefill with” dropdown.

Use a particular layer a lot?  Save it to your account so that it’s always available.