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Omar Eldaghar

Where can I find best DEM data?

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Omar,

Google Earth probably uses USGS or possibly their own proprietary data source for their elevation data, but you can't use their elevation data inside WMS.

If you're in the United States, the United States NED 10m data is a better source than the SRTM 3 arc-second data.  If you're outside the US, I have found the ASTER GDEM v2 Worldwide Elevation data (1 arc-second) to be more accurate than the SRTM 3 arc-second data (but it's still not really great data).  You can access this ASTER data from inside WMS using the following steps:

1. Select the Get Data from Map menu item or button.

2. Define your data bounds using the map locator and hit OK.

3. Select the Advanced button at the top of the Data Service Options dialog.

4. Under Popular Sources or Terrain Data, select "ASTER GDEM v2 Worldwide Elevation Data (1 arc-second)" and click Connect.

5. Define a filename to download your data and click Save.  Your data will be downloaded and loaded into WMS.  Right-click on the .tif file in the WMS project explorer and there's an option to convert it to a DEM.  Once it's a DEM, you can use it for watershed delineation.

Note that the upcoming verison of WMS (11.0) will have an option to download the best resolution elevation data for your area for anywhere in the world, whether inside or outside the US.

Let me know if you have any other questions.

Chris

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