Monday, June 3, 2013

Summit Views and Aerial Maps

I can finally announce the CalTopo Viewfinder (working name), a new page that shows a simulated view for any spot in the lower 48.  Play with it today by right-clicking on the map background and choosing "View From Here", or simply go to

The default view is a ground-level wireframe with peak names, which is great but hardly new. has been doing that for a while, and packages the functionality in a nice mobile app to boot.

Looking towards the palisades from Big Pine, CA
Step 1 was to add aerial imagery to the view, which helps give a better sense of what you are (or will be) looking at:

The view from Mt Tamalpais, CA
You could do this in Google Earth by importing a KML file with all the local summits, but Earth's ground-level view can be frustrating to work with.  And you can't zoom in on distant summits, only move towards them.

I noticed that it was hard to drop the "eye" exactly where you want it, and sometimes the actual summit would obscure part of the view.  So I added an option to control the eye altitude.  And I kept making it taller and taller, eventually taking it up up and away into the stratosphere.  The rendering math I'm using assumes a small eye elevation relative to the radius of the earth, so this isn't a perfect representation of what you'd actually see from that height, but I do think it provides some new and interesting terrain visualizations.  Click the linked captions for large, interactive versions:

East Slope of the Sierra

Glacier National Park

West Slope of the Sierra

Front Range

North Cascades National Park

It may be personal bias, but for some uses I prefer the zoom in from a fixed point approach used by CalTopo over the zoom by panning approach used in Google Earth.  The perspective feels more like the relief models found in NPS visitor centers, and makes it easier for me to wrap my brain around large-scale terrain features.

This is still under active development.  Beyond performance improvements, the USGS summit data could do with some refining as peaks are sometimes off by several hundred meters.  And, I hope to be able to offer custom print-on-demand posters that capture these high-altitude views in a nice, wall-friendly format.


  1. Nice work Matt...great to see you keep adding new features!

  2. Hello Matt,

    The content and information you provide on CalTopo is amazing, and you keep adding great features like this! I appreciate all of the effort that you put into the site.

    Are you aware of any map databases or overlays of trails? I was hoping the new USGS topo maps would have this feature, but it appears they don't have any trail data for now at least. It would be great to have an easy way to overlay trail data on top of imagery or different map types, but I can't seem to find any good sources for this.

    Thanks again!

    1. I'm not aware of any comprehensive ones - if I were, I'd build a layer out of them. While the NPS and USFS both have public trail data, it's mostly grouped at the park/forest or regional level. Building a nationwide layer would require collecting all of these individual data files, agreggating them into a common schema, and de-duping overlapping trails. This is something you'd expect the USGS to be all over, but as you can see from their latest maps they seem to be lagging here.

      The other option is to use OpenStreetMap trail data, but that still has a lot of errors and omissions - although it's constantly improving. At some point I'll probably try creating a mostly-transparent trails layer off this dataset, but it would be time intensive and I don't think the OSM data is good enough yet.

  3. Thanks for the information! I have checked out the OSM data, and you're right about it lacking still. Some places it is quite good, others not so much. Maybe the USGS will update their new topos in the future.

    Thanks again!

  4. Hi Matt. I'm just exploring your site, which seems wonderful, but do you have topo for BC, Canada and do all your actions work for BC?