DRGs - Digital Raster Graphics
Please choose which block degree:
CDs of quads by county are now available. Email Steve.
LizardTech - has a free viewer that allows you to save all
or part of a .sid file to geotiff format.
County DRGs
are now available. Some counties along the middle and western portions of the
state are split into two .sid files, this is because half the county was
produced by USGS and the other portion by TVA. The X-resolutions did not
match so a seamless countywide file was not possible for 10 counties: Bolivar,
Claiborne, Clarke, Copiah, Issaquena, Jasper, Simpson, Smith, Warren, and
Washington. Please download both sets of files for these counties. DRG's are digital copies of 7.5
minute - 1:24,000 topographic maps published by the U.S.Geological Survey.
The USGS produces their DRG product by scanning paper copies of the map at
500dpi and then resampling them to 250 dpi.
USGS topographic maps covering Mississippi were published over a number of
years, with the most recent original versions and updates ranging from the
early 1960's to mid 1990's. The DRG's are output as geotif image files
georeferenced to UTM NAD 83 coordinates.
The MARIS staff has reprojected the DRG tif files into the MSTM projection
and then compressed them using MrSID compression software. The files are stored
by blocks designated by degrees of latitude and longitude (for example - 3390
identifies maps with a longitude of 33 degree and longitude of 90 degrees,
etc.). Individual file names follow the USGS naming scheme (3390a1.sid, 3089g3.sid,
etc.) MrSid desiginates the image file as a .sid file with an associated
.sdw file as a world geo-reference file. The .sid file is binary while the
.sdw file is ASCII.
These files are NOT available in any other format or projection from the MARIS Technical Center.
The reference lists below can be used to determine the file name and degree
area that you need.
The MARIS Technical Center has mosaiced goups of indiviudal DRG's together
to produce county-wide sets of seamless DRGs that are available via CD-ROM
by filling out the online order form.
If there are any general questions about DRGs and downloading or acquiring
the data through other means, please contact Steve Walker at swalker@ihl.state.ms.us or 601-432-6149.
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