DOQQ example of Benton, Kansas
color aerial with 1 meter resolution
A secondary source of aerial photography is the
United States Department of
Agriculture Service Center Initiative, or
GeoSpacial Data Gateway. The
Geospatial Data Gateway provides Internet-based, one-stop-shopping for natural
resource or environmental data. It offers a single access point to a vast store
of data, allowing you to browse through what is available, choose only the area
that is needed, order it in the desired projection and format, and have it
automatically delivered electronically or via CD. The color aerials from this
website are also one meter resolution and have better contrast than that of
black and white photos as shown above.
The most sought-after resolution for aerial photography to
be used as a base layer for printed maps is 6-inch, high resolution. This can be
somewhat difficult to come by but when it is acquired, it benefits the utility
(city or RWD) by providing better representation of in-the-field conditions.
1 meter resolution
6 inch resolution
Above: comparison between 1 meter and 6 inch resolution
using the City of Olpe.
DRG example of Harrisburg, Pennsylvania
Digital Raster Graphic
A digital raster graphic (DRG) is a scanned image of a U.S. Geological
Survey (USGS) standard series topographic map, including all map collar
information. The graphic portion of the map is geo-referenced to the
surface of the earth and fit to the Universal Transverse Mercator
projection. The horizontal positional accuracy and datum of the DRG
matches the accuracy and datum of the source map. The map is scanned at a
minimum resolution of 250 dots per inch. A good source for the DRGs is the US
Geological Survey's website.
The DRG's have been found difficult to use for KRWA's GPS mapping
purposes. They are scanned and formatted at a 1:24,000 scale and are
limited to that scale. The graphic and text "comes apart" when blown to
the scale utilized in mapping rural water districts, 1:500.