Custom slope angle overlays for Google Earth

[SlopeAngleMaps_Dude]

For years I've wanted a color-coded slope angle overlay for Google Earth to help me plan my various ski adventures in the backcountry, but no such layers seemed to be available anywhere. Finally, I decided this needs to be done.

I developed a method to make some nice slope angle overlays for any mountain/region in the U.S., and I can generate these for anyone interested. See my website for more info:

www.SlopeAngleMaps.com

While I'd love to provide these data overlays as a free service, the data processing requirements are too heavy for me to simply take requests. To help compensate for the time involved in producing the overlays, I charge a low fee proportional to the amount of data processed.

I've been using the overlays so far this season for route planning, and to get an idea about what a mountain will really be like before I commit to it. This is a great tool for quickly determining the safest routes around avalanche terrain.

I know there's been some chatter on this forum about this for a while now, so hopefully this will help some of you out.

Let me know what you think.

[SILENCER]

This...looks extremely cool.

[davieboot]

This is actually a decent idea, but there should be a better color scale. It is tough to pick out "prime time" slopes around 38 degrees. A bigger spectrum (blue to green to orange to red, for example) would make it much better.

[SlopeAngleMaps_Dude]

Thanks for the input.

The color scale is a tough question. Strictly speaking, the more colors you can pick out, the more information you have about the slope. On the other hand, the overlays get messy and painful if I use a full rainbow scale.

I chose the blue-purple scale because it is pretty mellow on the eyes, which makes it pretty easy to follow.

As for highlighting primetime-38-degrees, that could be done, but I'd hate to make this angle stand out too much. There are, of course, plenty of avalanches on slopes not equal to 38 degrees. That said, maybe I'll make a scale that gets hotter in the middle, then cooler towards both ends. That would portray things nicely I think.

[skinipenem]

Absolutely fantastic!

[davieboot]

As for highlighting primetime-38-degrees, that could be done, but I'd hate to make this angle stand out too much. There are, of course, plenty of avalanches on slopes not equal to 38 degrees. That said, maybe I'll make a scale that gets hotter in the middle, then cooler towards both ends. That would portray things nicely I think.

You are obviously correct. A scale that gets hotter in the middle would be ideal, I think, as long as you could still easily differentiate between low angle and very steep slopes at the end of the spectrum. Even 3 colors, with the middle color hitting the 33-43 range would do the trick I think.

Still digging the concept.

[_Aaron_]

What happened to looking at a topographical map for this kind of info?

[pde20]

Very cool. I was just pondering whether something like th is would be possible on a tour yesterday. I'm not competent enough w/ GIS to figure it out, but glad to see that someone is.

[SlopeAngleMaps_Dude]

Based on input from users, I added an option for a second color scheme. This one is much more colorful and allows you to pick out any angle you want easily. See:
http://slopeanglemaps.com/info.html#format

Aaron, putting the good 'ol days behind us, a topo map can give you a pretty good idea of how steep a slope is compared to others around it, but it's a strain on the eyes, and not all that fun, efficient, or accurate of a way to figure out slope angle (unless you're REALLY good).

I think my overlays provide more information faster, which can be really nice when you're planning a trip and trying to decide the best route up, down, around, between, etc.

Not that topo maps are outdated, this is just another tool.

[_Aaron_]

^^ Gotcha. Looks pretty cool. How accurate and over what scale are you calculating? Say for instance on a topo with 40ft intervals I can calculate a avg slope angle for every 40ft on the map. What are the intervals on your maps? (if that question makes sense to you)

[zeroforhire]

Great stuff. You should post in some mountaineering forums as well. I am sure those guys would like this.

[SlopeAngleMaps_Dude]

For the continental US, the data resolution is about 10 meters. So I calculate the slope angle for every elevation point using the surrounding points in a finite difference.

This means there is a slope angle point every ~30ft. Each data point is represents the average slope angle over a ~30x30ft square, so of course my overlays can miss small pockets that may present some avalanche hazard. Still, they provide a nice detailed representation of the average slope.

I find the data resolution just good enough to pick up most of the small terrain features. Also, the overlay picks up and highlights many features that would go entirely unnoticed in Google Earth, and especially those that would go unnoticed on USGS contour maps.

[HustleHard]

hey slopeangle,
you a GIS guy?

[khakis]

Also, the overlay picks up and highlights many features that would go entirely unnoticed in Google Earth, and especially those that would go unnoticed on USGS contour maps.

This is probably not true...unless you've got a source for LIDAR or custom-flown elevation data, the USGS DEMs you are building these layers from were digitized off of 7.5 minute USGS topos...so the topos are actually more accurate.