USGS 7.5 Minute Digital Elevation Files of California - Description |
![]() |
This site provides access to a set of digital elevation model (DEM) files of California. The files are located at a California State University Northridge Department of Geography FTP server.
For a comprehensive description of the USGS DEMs, see http://edc.usgs.gov/products/elevation/dem.html at the USGS Global Land Information System server.
The 7.5 minute files (a.k.a. 30 meter DEMs) are the highest resolution DEMs currently available for a major percentage of the U.S.: see http://edc.usgs.gov.
The resolution is exactly 30 meters on the ground, which is approx. 1 arc second on the meridian. The data points are gridded on a Universal Transverse Mercator basis (UTM, easting and northing) rather than a geographical basis (longitude and latitude).
This has a major advantage: towards the high north the resolution on a parallel does not increase due to the meridians converging. No need to downsample the Alaska area; homogenous resolution all over the area.
However, a major drawback: contiguous DEMs can't be easily tiled, because the data point rows and columns do not have a straightforward continuation on the neighbor DEM. See http://edc.usgs.gov/products/elevation/dem.html for details.
From the Overview map of California, locate the one degree quadrangle you are interested in. By clicking it, you will get a zoomed-in map subdivided into 7.5 minute quadrangles. Each can contain a link to the gzipped DEM file behind.
This is the legend for the one degree maps:
The files have been compressed with the GNU "gzip" utility. The gzip program is available via anonymous FTP at many sites:
gzip for UNIX: http://www.google.com/search?q=gzip+UNIX
gzip for MAC: http://www.google.com/search?q=gzip+MAC
gzip for MSDOS: http://www.google.com/search?q=gzip+MSDOS
This page was last updated:
05/19/09.
Copyright © 1996-2009 Martin D. Adamiker's. All Rights Reserved.