Among the highest quality DEM data you can get to go with a standard USGS 1:24K topo map is 10-meter SDTS DEM data, with heights specified to the nearest 0.1 meters (though the altitude accuracy of the DEM likely doesn’t warrant that resolution). I find it superior to the 10-meter NED data provided by the USGS Seamless Server, with fewer artifacts, although the SDTS format isn’t as well-supported as the DEM formats available at the Seamless Server. The SDTS DEMs are also in UTM NAD27, same as typical for USGS topo maps, versus the geographic projection for Seamless Server DEMs. There are a fair number of pay sites on the Web that offer these SDTS DEM files for a price, but there is one website where you can download them for free.
The GIS Data Depot has gone through some changes over the years, but is still around. It offers not just SDTS DEMs but a host of other GIS data, some free, other not free (you can often find the paid data for free elsewhere on the web). Data is classified as “statewide” or “countywide”, and you’ll find the SDTS DEMs in the “countywide” sections, listed in the Digital Elevation Models (DEM) – 24K section under the 1:24K topo map name whose area they cover (offered in both 10-meter and 30-meter resolutions) . The catch with the free “Normal” downloads is that they are at slower speeds than the paid “Premium” download (appears to be roughly 10 kilobytes per second or so).
FYI,
the 3 USGS partners are the only official USGS distributors of the DEMS – a totally hideous decision by the USGS! FYI, but, these data are easily and freely available for free download via many county, State and other GIS clearinghouses. The following detailed resources lists a number of free DEM resources:
– free USGS data – http://www.gisuser.com/content/view/607/28/
– A GISuser Primer on the National Elevation Data Product (NED) – http://www.gisuser.com/content/view/1396/28/
– FGDC Suggested State Clearinghouse Websites – http://www.gisuser.com/content/view/4588/28/
– State GIS Clearinghouse Directory – Update, July 2004 – http://www.gisuser.com/content/view/2379/28/
these articles offer up a ton of suggested resources where you can grad DEMs in DEM format rather than the painful sDTS and the data are free and available via FTP or speeds much faster than 10 or even 5 KBPS (as offered by commercial usgs partners) how painful would that be!
I’ve posted on some of these before, particularly the USGS Seamless Server. But the NED data can sometimes have odd artifacts, due either to re-sampling to geographic coordinates or matching up borders. SDTS can be a painful format, but the quality is very high. And the ADTI website offers SDTS DEMs at high download speeds.
Does anyone know of any DTM data for the UK?
There’s 90-meter SRTM data available for a good part of the world, but for higher resolution, you either have to buy it or digitize it yourself from a topo map.