I am curious about using National Elevation Data Set (NED) information available from the USGS to prepare rough, preliminary contour maps. It seems to be free and possibly more accurate than the USGS maps for our area (and maybe even our 5' contour maps fom the county).
Does anyone do this? If so, do you have a procedure you have found to be effective?
Thanks!
Preliminary Contour Maps
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Preliminary Contour Maps
by Tony » Tue May 27, 2008 2:57 pm
- Tony
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- Joined: Fri Dec 21, 2007 1:24 pm
- Location: Cleveland, TN
by TerryS » Thu Jun 12, 2008 1:38 pm
Keep a few things in mind:
NED data may just be comprised of DEM data, but just made available in a different format (seamless vs. quads).
DEMs may just be interpolated from USGS contours.
The default is 10m grids...so it can easily miss significant features. (I am in a flat coastal area and this digital data misses ditches and roads that greatly influences drainage)
They may use more acurate sources..read the metadata...it may contain clues.
I use this information for recon and for analyzing off-site drainage that is definately outsied the scope of our topo.
One just needs to know what one is dealing with.
NED data may just be comprised of DEM data, but just made available in a different format (seamless vs. quads).
DEMs may just be interpolated from USGS contours.
The default is 10m grids...so it can easily miss significant features. (I am in a flat coastal area and this digital data misses ditches and roads that greatly influences drainage)
They may use more acurate sources..read the metadata...it may contain clues.
I use this information for recon and for analyzing off-site drainage that is definately outsied the scope of our topo.
One just needs to know what one is dealing with.
- TerryS
- Posts: 34
- Joined: Mon Nov 05, 2007 4:07 pm
- Location: Delaware
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