流域境界を決定するために必要なNED 30をどのように見つけますか？

Question

<\/HEAD>ワシントンDCで流域を区画しようとしており、そのためにNED 30が必要です。どのように入手できますか。National Map Viewerで見つけられることは知っていますが、ダウンロードセクションに約200のファイル名があり、どれをダウンロードすればよいかわかりません。<\/P> ありがとうございます<\/P><\/BODY><\/HTML>

ChrisDonohue__GISP · Accepted Answer

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