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Introduction to Map Layers for Backcountry Navigation

GIS Data Layers

Most modern maps are generated from multiple map layers stored in Geographic Information Systems (GIS). Each map layer represents a different group of geo-referenced data points that are superimposed one on top of the another to create a composite map image. For example, Google maps using this technology to display businesses and public building on top of street maps. It’s also used widely in business applications to visualize relationships between different data layers and geographic areas.

Many modern phone-based backcountry navigation apps including Gaia GPS, Guthook’s Guides, and ViewRanger use map layers to display different views of the same geographic areas and hiking routes. Map layers are also used by Caltopo.com, a free and very powerful web-based mapping application that lets you use incorporate you own data layers.

One of the most powerful features in Caltopo and other navigation apps is the ability to switch between multiple base maps of the same areas, including satellite imagery, so you can view and compare the same route using different types of backgrounds maps. For example, I can draw a hiking route to climb a mountain and then superimpose it on top of different backgrounds that emphasize different aspects of an area to help visualize what I’m likely to encounter on foot.

A hiking route displayed on top of 4 different base layers
A hiking route displayed on top of 4 different base layers

These base layers starting from top left, clockwise are: USFS 2016, Satellite Imagery, USGS 1885-1912, and Google Terrain:

  • the USFS (United States Forest Service) 2016 map is very up-to-date and includes nearby trailheads and roads
  • the Satellite imagery is from 2013-2015 and probably based on NASA imagery which is published into the public domain
  • the USGS (United State Geological Survey) 1885-1915 is a historic map that shows me what the area looked like 100 years ago
  • the Google Terrain map is probably fairly recent and derived from the current USGS Topographic National Map. It’s hard to know for certain, but topography changes fairly slowly compared to human artifacts like buildings, trails, or roads, so it’s probably good enough for navigating.

One of the thorniest issues with backcountry navigation today is knowing which digital base maps and data layers you can trust to be up to date and what you can’t. Digital map publishers and the apps that use digital maps don’t go out of their way to provide this information for you and the copyright notices published on digital maps or map layers rarely correspond to the dates in which the data was gathered. I’ll cover this topic more in another article.

You best bet is to carry a topographic map created by a local map publisher or outdoor organization that has a vested interest in publishing reliable maps. Maps published by national publishers, like National Geographic, are often based on outdated data from last generation USGS maps. It can also pay to carry or plan your trips with multiple paper maps as a way to check or augment the accuracy of digital sources.

Written 2018.

6 comments

  1. In the military this is called a Modified Combined Obstacles Overlay (MCOO). Layers like vegetation, hydrology and trafficability (how the slope and soil composition affect mobility) are added to the map in order to improve planning.

  2. It’s why I have several GPS apps on my iPhone.
    If I’m at all not clear about the trail, I’ll compare what the different apps show.
    I use Gaia, Guthooks, and Maps3D.
    They’re usually pretty close, but sometimes Gaia will show details that Guthooks doesn’t, or vice versa

  3. One other source to consider…many state and local governments have GIS websites and even downloadable shapefiles of terrain and other features. While not a lot of software can handle these, Google Earth Pro (which is free) can open them. I used this recently, for example, to find a particularly tricky off trail route in a wilderness area where all other topo was way off and led you down the wrong path.

  4. While I enjoyed this information and do recognize its value, especially for professional endeavors such as military use and other industry sectors, as a backpacker or hiker it is an abundance of information that seems redundant for planning a backpacking or hiking trip. I usually get myself a good topographical map of the area I plan to hike and preferably, get this map from a local geographic map store dealer in the area where the trail is located. Oftentimes the map dealer personnel know information about the trail. If I desire additional information I go to the local Forest Ranger station to meet with personnel there who often know of conditions of trails and other information as to what I may encounter. Again, it is not my intent to denigrate this excellent information, but as a hiker or backpacker planning an outing going to this extent of getting this level of information seems superfluous; unless I am involved deeply in some professional endeavor such as the military, prospecting, planning an extensive period in the backcountry, oil, gas, timber exploration or whatever, I see little need for all this information to plan a backpacking trip or to do a day hike.

  5. If you ever hike off-trail or backcountry ski, you’ll want this kind of information. Most US hikers never venture far from trails, but go anywhere where you can’t follow signs or blazes, and you need this. For example, I bushwhack a lot of trail-less peaks in the east. These map layers are invaluable for planning routes. Want to know where the avalanche zones are for backcountry skiing, use slope shading.

  6. Another great tool for route visualization, Google Earth, can display CalTopo layers on its 3D landforms. This can be a huge assist in planning an off-trail route. You do need to be a paid subscriber to CalTopo to get layers capability beyond your lines, polygons and waypoints. Exporting a network linked KLM fie and opening it in Google Earth provides a live link to your CalTopo map, so that updates to the map are reflected in real time in Google Earth. Pretty cool!

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