Tech Tip: External Map Sources for CalTopo

|| GUEST AUTHOR||

Tyler Jaszkowiak is a trail runner, mountaineer, rock climber, and software engineer based in Seattle, WA. A few weeks ago Tyler showed me how to import data into Caltopo and overlay the information as a layer. I knew that this would be an extremely useful post, so I asked Tyler to do a write-up for my blog. Without further ado…

As many backcountry travelers know, CalTopo is an exceptional tool for planning and visualizing routes. The tool allows users to overlay numerous map layers and GPS data. For example: I will often use a USGS topo map as a base and overlay a semi-transparent layer of recent high-resolution satellite photos from the European Space Agency’s Copernicus Programme. This allows me to understand where I may encounter snow on a planned route.

However, there is map data available on the web that is not part of CalTopo’s offering and would be similarly useful in route planning, such as Snow Depth estimates. CalTopo does offer the ability to import maps from external sources, but it can be confusing. In this post, I will share detailed instructions on how to import my favorite government-provided data into a CalTopo layer.

First: the basics. At the bottom of the left-hand menu on any CalTopo map is an “Add New Layer” button. Clicking this opens a dropdown from which you will select “Custom Source.” This opens a dialog box. Here is where we’ll configure our custom layers and use either the “Save” button in the lower right to save a layer to a specific map or the “Save To Account” button in the lower left to save a layer to your CalTopo account.

NOAA Snow Depth

One layer I find useful is the snow depth estimate mentioned above. The key for this map is layer 3 found in this legend. Units are in inches. Below is a screenshot of the snow depth data overlayed on a topo map at 50% transparency. You can see that snow is absent in the urban centers and many of the river valleys, but still exceeds 98 inches on the Cascade crest. I have found this to be very useful in trip planning, especially below treeline, where recent satellite photos may not show the snow.

To import this map, use the following settings in the Custom Source dialog:

NOAA Snow Water Equivalent

This layer shows the amount of water trapped in the snowpack – the equivalent depth if it were melted. The key for this map is layer 7 found in this legend. Units are in inches of water. In the screenshot below, we can see that the Cascades are currently trapping dozens of inches of water at high elevations.

To import this map, use the following settings in the Custom Source dialog:

USGS Bedrock

This map shows the underlying rock type in geologic units across the lower 48 United States. The key isn’t particularly useful to me as a non-geologist. But as a climber, I can see in this screenshot that the “good” rock type found at Little Si extends up the North Fork of the Snoqualmie to several other areas that might offer fun climbing.

To import this map, use the following settings in the Custom Source dialog:

NLCD Land Cover

This map shows the land cover of the United States according to this key. Most topo maps will show this as well, but it can be nice to include a more vibrant version at times.

To import this map, use the following settings in the Custom Source dialog:

Washington State Roads – Present & Abandoned

For this example, I’ll walk through the process I go through to find and configure these layers in more depth. There are many repositories of government-provided geospatial data. In Washington State, the repository is found at http://geo.wa.gov/. I am interested in finding road data, so I’ll select the “Transportation” category and search for datasets that include the word “Road” in the title. Eventually, this leads me to the page on WA DNR Orphaned and Abandoned Roads. The “API Explorer” tab here will tell me how to access the data.

The right-hand-side of this page gives a query URL. I have done this enough that I know shortening this URL by ignoring everything after the word “MapServer” (so https://gis.dnr.wa.gov/site2/rest/services/Public_Forest_Practices/WADNR_PUBLIC_FPAMT_Main/MapServer) will take me to the documentation on the map service. Here I can find a link to the legend and a list of layers this service provides.

In CalTopo’s “Custom Source” dialog, if I paste this MapServer URL into the “Auto-configure URL” field and hit the “Go” button adjacent to it, CalTopo will return a list of the available layers. In this example, I’ll pick 3, 4, 5 so I can get all current and abandoned roads in Washington state. CalTopo figures out the Type and URL Template for us.

All that’s left to do is save the map!

Above, you can see the view of the state-managed land at Taylor mountain populated with the abandoned and active roads from this State data – many of which are not accounted for in the OpenStreetMap data that CalTopo uses to draw trails on its MapBuilder Topo map.