topic Extract Min/Max elevation from DEM? in Data Management Questions

Extract Min/Max elevation from DEM?

TomKearns — Tue, 18 Jun 2013 19:21:30 GMT

If I create a polygon and use it to run Zonal Statistics over the DEM (as the input raster) will I end up with accurate min and max elevations?

Rephrased: Are DEM's accurate elevation measures or are they scaled numbers (not measures in meters) assigned to show relationships?

Thank you in advance.

Re: Extract Min/Max elevation from DEM?

curtvprice — Tue, 18 Jun 2013 20:33:57 GMT

Are DEM's accurate elevation measures or are they scaled numbers (not measures in meters) assigned to show relationships?

This totally depends on your DEM dataset. For example, sometimes elevation datasets are shared using centimeter values so they can be stored as integer (for better compression) while still preserving .01 meter precision.

Re: Extract Min/Max elevation from DEM?

TomKearns — Tue, 18 Jun 2013 20:48:47 GMT

Thank you for the reply. I am using a 1 arc second, 30M resolution DEM.

Another way to ask my question would be "do I need to manipulate a DEM to convert it to real measures".

Thanks, again.

Re: Extract Min/Max elevation from DEM?

curtvprice — Tue, 18 Jun 2013 20:54:39 GMT

I am using a 1 arc second, 30M resolution DEM.

Another way to ask my question would be "do I need to manipulate a DEM to convert it to real measures".

The metadata (or readme files) that accompanied the raster data should tell you what the z units are. If this is downloaded NED data from the USGS National Map, the z units are in meters.

The elevation data from National Map is delivered in geographic coordinates. If you are doing analysis that involves measurement of distances or areas, before you start the analysis you should project the raster to a coordinate system that will support your analysis (for example, UTM). .

Re: Extract Min/Max elevation from DEM?

TomKearns — Tue, 18 Jun 2013 21:06:29 GMT

That is exactly the help I needed. Thank you.