GISuser Guide to downloading Free 7.5 minute DEMs

Are you searching for standard 7.5 minute USGS DEMs? You may have already discovered that the USGS no longer makes these data available for free download via FTP or any other mechanism for that matter.

They do however, make these data available via several strategic business partners. A search of the USGS site should yield pointers to these resources. This has been a rather “Hot” issue, to say the least, however, we’ve stumbled onto a wondeful resource that you will appreciate. This Canadian-based server hosted by WebGIS is serving up all the USGS 7.5 minute DEMs for FREE… no user registration required, no logins, no throttled-back throughput. Simply click on a map and start your download.

To access 7.5 minute USGS DEM data, please select a State on the map below. Conversely, for a simple way to access a DEM for a specific area (lat/long required) use the ATDI DEM download application (SDTS format) – see http://www.atdi-us.com/SDTS_DL_b.htm

UPDATE: Since we first published this piece we have received some helpful information regarding these data… please read prior to downloading. The data accessible here are not standard USGS SDTS data, but rather, they have been coverted to DEM format. Something else to keep in mind, the naming conventions used are different than what you might expect from standard USGS data. This source uses the first four characters of the .ddf files as the file name and this could potentially be problematic as that identifier is not necessarily unique. Fianlly, USGS “.

WAORIDMTNDMNCANVUTAZWYCONMSDIANEKSWIMIILMOOKTXARLAINOHKYTNMSALGAFLSCNCVADCWVPAMDDENJRIMACTVTMENHNYVIPRHIAK

Note: The image used to create this map was provided by the USGS 

A number of State spatial data clearinghouses also have 7.5 minute DEMs available for free download, however, availability varies from State to State – See the State Resources listed in this arrticle for more DEM download nodes.

7.5-Minute DEMs correspond to the USGS 1:24,000- and 1:25,000-scale topographic quadrangle maps, and are available for all of the U.S. and its territories. They are cast to the Universal Transverse Mercator (UTM) projection system and are referenced to either the North American Datum (NAD) of 1927 (NAD27) or the NAD of 1983 (NAD83). Most files will have a grid spacing of 30 meters, but 10-meter grids are also available for some locations. The average file size of a 30-meter DEM is 1.1 megabytes and 9.9 megabytes for a 10-meter DEM. They are available in Native and Spatial Data Transfer Standard (SDTS) format.

Some suggestions from our friends at the USGS Earth Science Information Center. If you want to move away from SDTS DEMs completely, you might want to consider looking at the NED (National Elevation Dataset). NED is seamless and users have a choice of download formats. See http://seamless.usgs.gov – Elizabeth McCartney of the USGS tells us we’ll be “especially impressed with the high-res urban DOQQs.”

McCartney also informs us that The National Map website is also coming along quite nicely. It doesn’t have download capabilities yet, but it will [stay tuned!] McCartnet pointed out the following attributes of the National Map:

  • It has quite a nice print function if you just want a nice picture of the area you are looking at in a .pdf file.
  • Some feel its better than Terraserver because you can overlay roads (and more) over the DOQQs.
  • The DOQQs and DRGs are currently being pulled from Terraserver into The National Map.
  • See http://nationalmap.usgs.gov/nmjump.html

Suggested Resources:

 

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