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How to find NED 30 needed for a watershed delineation?

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12-04-2014 01:56 PM
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FaridAria
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‎12-04-2014 01:56 PM

I am trying to delineate a watershed in Washington DC and I need NED 30 for it. How can I get it. I know it can be find in National Map Viewer but I go to download section there are about 200 file names and I can't figure out which one to download.

Thanks

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ChrisDonohue__GISP
by MVP Alum
MVP Alum
‎12-04-2014 03:59 PM

I'm not an expert on DEM's and their downloads, but here's some ideas based on my likewise flailing around on my infrequent downloads of them:

An idea - there are several options in Download Data section of the National Map Viewer.  One is "Click here to draw and download based on a bounding box."  This could help limit your selection.

Also, I believe the 30 meter DEM's match the same extents of USGS 24K Topo Quads (though I could be off on this).  This may offer another way to determine which ones you need - there is a reference layer that can be displayed for the 24k Quads.

Then the crux issue - once you go to the Download function, it returns a long list of different files, making it difficult to figure out which one needs.  I believe for 30meter DEM's the files you want to download are just the ones listed as "1 arc-second" under the Resolution column. However, I'm not 100% sure on that - maybe someone who is more knowledgeable can chime in on that?

Hope this helps,

Chris Donohue, GISP

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ChrisDonohue__GISP
by MVP Alum
MVP Alum
‎12-04-2014 03:59 PM

I'm not an expert on DEM's and their downloads, but here's some ideas based on my likewise flailing around on my infrequent downloads of them:

An idea - there are several options in Download Data section of the National Map Viewer.  One is "Click here to draw and download based on a bounding box."  This could help limit your selection.

Also, I believe the 30 meter DEM's match the same extents of USGS 24K Topo Quads (though I could be off on this).  This may offer another way to determine which ones you need - there is a reference layer that can be displayed for the 24k Quads.

Then the crux issue - once you go to the Download function, it returns a long list of different files, making it difficult to figure out which one needs.  I believe for 30meter DEM's the files you want to download are just the ones listed as "1 arc-second" under the Resolution column. However, I'm not 100% sure on that - maybe someone who is more knowledgeable can chime in on that?

Hope this helps,

Chris Donohue, GISP