Summary of Spatial Data Types
Links to Spatial Data Web Sites
Summary of Spatial Data Types
Digital orthophotos are aerial photographs
with tilt and relief displacement removed from them (i.e., they
are planimetrically correct). Therefore, ground features displayed
on the orthophoto are in their true ground location. Direct measurement
of distances, angles, and areas from the orthophotos may occur because
orthophotos are planimetrically correct. Digital orthophotos are
generally available in black-and-white and color infrared with 1-meter
ground resolution. Orthophotos are incredibly useful GIS layers.
They are often used as backdrops for vector data like roads, hydrography,
and parcels, and as a tool for updating and collecting vector data.
For more information on digital orthophotos, check out the following web
metadata for digital orthophotos
Digital orthophoto fact sheet
To order digital orthophotos, check the Global Land Information System
Digital Raster Graphics (DRGs), produced by USGS, are scanned, geo-referenced USGS standard series topographic maps. DRGs are also used as backdrops for vector data, and they are used to revise and collect digital data. The Land Information and Computer Graphics Facility has processed the DRGs that lie along the Lake Michigan and Lake Superior shore here in Wisconsin. Click here to see a map of the DRGs available from LICGF and to learn more about the processing performed on them. For more information on digital raster graphics, check out the following web sites:
DRG Program Information
DRG fact sheet
To order digital raster graphics, check the Global Land Information System
Digital Elevation Models (DEMs) are data sets comprised of terrain elevations for ground positions at regularly spaced horizontal intervals. The highest resolution DEMs available for the United States are the 7.5 minute DEM series available from the USGS. This series has a resolution of 30 meters (i.e., the interval between each ground point is 30 meters). While this resolution is sufficient for watershed delineation and other such tasks, we believe it is too coarse to be used in coastal applications. For more information on digital elevation models, check out the following web sites:
metadata for DEMs
DEM fact sheet
To obtain free 1:250,000 DEMs, check US GeoData
To order any other DEMs, check the Global Land Information System
Digital Line Graphs (DLGs) are digital vector files representing cartographic information. USGS derived these files from aerial photographs and hard copy maps using manual and automated digitizing methods. Large-scale DLGs are produced in 7.5" units that correspond to 1:24,000 topographic quadrangles. Features represented in the large-scale DLGs include political boundaries, hydrography, Public Land Survey System, transportation, hypsography (elevation), vegetative surface cover, nonvegetative surface cover, and survey control and markers. DLGs are also available in 1:100,000 scale and 1:2,000,000 scale versions. For more information on digital line graphs, check out the following web sites:
metadata for DLGs
DLG fact sheet
To obtain free large-scale, 1:100,000, and 1:2,000,000 DLGs, check US GeoData
TIGER (Topologically Integrated Geographic Encoding and Referencing System), developed by the U.S. Census Bureau to support the decennial census, is a geographic database that covers the entire United States. The Census Bureau, along with USGS, created the TIGER database in the 1980s. The USGS scanned roads, railroads, hydrography, and transportation layers from 1:100,000 USGS topographic maps. Then, the Bureau integrated the layers into one topologically consistent file. For the urban areas, the GBF/DIME files created in the 1970s and updated in the 1980s were integrated into the TIGER database. The public can order a product called TIGER/Line files from the Bureau or other vendors. These line files, extracted from the TIGER database, contain the boundaries of legal, administrative, and statistical areas for every county, parish, borough, and census geographic area in the U.S., U.S. Virgin Islands, Puerto Rico, Hawaii, and the Pacific Island Territories. Alternatively, some of the TIGER/Line files can be downloaded free of charge from the Internet. For more information on TIGER or to download TIGER/Line files, check out the following web sites:
The TIGER Page
at the Census Bureau
Archive of Census Related Products (including 1992 TIGER data)
DDCarto (Demographic Data Cartogram Service) --Download Census data in Atlas GIS, ARC/INFO, or MapInfo format for every county in Wisconsin
The Wisconsin DNR Geographic Services section has 5 CD-ROMs of
digital spatial data available for purchase.
to learn more about the CD-ROMs, including instructions for ordering the
discs, from DNR.
Last modified by David Hart on August 30, 2000. Originally developed by David Van Riper in .