# Slope Angle Estimates - over what distance and in what direction(s) from a point is slope angle estimated?

Note: I'm not asking for any trade secrets or proprietary information, but for general knowledge useful for a person who uses CalTopo slope angle estimates.

- As I understand slope angle, 2 points are needed to estimate a slope angle. Is this correct?

- As I understand slope angle, 2 points ("the run"), and the elevation difference between the 2 points ("the rise"), are needed to estimate slope angle. Is this correct?

- For any specific geographic coordinate/location/waypoint, how does CalTopo determine the 2 points used to estimate slope angle?

Thank you!

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Support Staff 1 Posted by

rmarcuccion 10 Mar, 2020 11:13 PMTom,

You have the basic idea, the reality is just WAY more complicated than that. We get our data from publicly available datasets from the USGS. Here's a recent blog post post regarding some new high resolution data: http://caltopo.com/about/2019/12/20/high-resolution-elevation-data/

With that raw data, we create a model, which we use for contour lines as well as slope angle shading. CalTopo has created a proprietary algorithm to analyze points in that model in relation to adjacent points, and create the slope angle shading you see on the map.

I hope that gives you a basic understanding of how the whole thing works.

All the best,

Rom

rmarcucci

closedthis discussion on 10 Mar, 2020 11:13 PM.Tom

re-openedthis discussion on 11 Mar, 2020 06:35 AM2 Posted by

Tomon 11 Mar, 2020 06:35 AMThanks!

rmarcucci

closedthis discussion on 11 Mar, 2020 04:46 PM.