This is a Digital Raster Graphic (DRG). A Digital Raster Graphic is a scanned image of a USGS topographic map. The image is georeferenced to the earth's surface and fit to the UTM (Universal Transverse Mercator) projection.
Monday, October 4, 2010
DOQQ - Digital Ortho Quarter Quads
This is a Digital Ortho Quarter Quads (DOQQ) map. DOQQs are digital aerial images produced by the United States Geological Survey (USGS). These maps can be found for every state and are organized by county (most of the time). These maps contain orthorectified aerial photography at a resolution of 1 meter. Image displacements caused by the tilt of the camera and terrain relief are removed from the derivation from a digitized perspective aerial photograph. This DOQQ is of Tennessee.
DEM - Digital Elevation Map
This is a DEM or a Digital Elevation Map is a digital representation of ground surface topography. DEMs are commonly built through remote sensing techniques and are often used in GIS (geographic information systems). This DEM depicts the Hood Canal.
Doppler Radar
Most people are familiar with this type of map, a Doppler Radar Map. However, as the site that this image was found on points out, the Doppler Radar Maps that we are most familiar with are actually "reflectivity images." With Doppler Radar, a radar pulse is sent out, the frequency is measured, and the results indicating the velocity of precipitation are represented through colors. Although there are no steadfast rules for color usage, the colors are often assigned similar to the actual shifts seen when the Doppler effect is applied to visible light...red, orange, and yellow indicates raindrops blowing away from the radar antenna; green, blue, and violet indicates raindrops blowing toward the radar antenna.
Dot Distribution Map
This is a Dot Distribution Map. This type of map uses a dot to represent the presence of the chosen feature. Spatial pattern in a Dot Distribution Map is displayed through visual scatter. This Dot Distribution Map depicts the population distribution of the United States based off the 2000 Census. This particular map is popularly known as the "Nighttime Map" because the background of the United States is displayed in black on a royal blue background with the white dots appearing as lights in the night sky. The "well-lit" areas of the map indicate the urban populations. On the wall-sized version of this map, each dot represents 1,000 people while on the page-sized version, each dot represents 7,500 people.
Sunday, October 3, 2010
Cadastral
A Cadastral Map is a map that depicts the value, extent, and ownership of land as a basis of taxation. This example depicts the property ownership boundaries for the Acland's and their neighbors.
Cartogram
A Cartogram is a thematic map. In a Cartogram, actual land area or distance is purposefully distorted as a way to represent the mapping variable being depicted. As the blurb for this specific example explains, the area of each state in this map is directly proportional to the number of electoral college votes for that state. The map also includes an inset of the geographic map of the United States for comparison. Furthermore, on the bottom of the map, the Cartograms for the previous three presidential elections are shown to represent the change in "allegiances" for the states.
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