Tuesday, April 3, 2012


     A Digital Elevation Model (DEM) is a data set containing elevation values either in raster data form or in a Triangular Irregular Network (TIN).  These data sets are commonly created through remote sensing techniques but can also be made through land surveying.  This data is also regularly used in a GIS and is the basis for relief maps. The example shown above is the DEM of the contiguous United States. With this DEM, we are able to observe the commonly known mountain ranges of the U.S. (the Rocky Mountains in the west and the Appalachain Mountains along the east coast).

Black and White Aerial Photos


     Black and white aerial photography is data gathered in the visible spectrum rather than in the infrared.  In this part of the electromagnetic spectrum, black and white color values are exactly what we see in the visible spectrum. This aerial imagery allows us to analyze large areas of either developed or undeveloped land in a variety of different spatial resolutions. This black and white aerial example shows the reconstruction of Johnstown, PA in 1891; two years after it was flooded.

Infrared Aerial Photo

Infrared aerial photos are very useful to reflect the health of vegetation and also bodies of water. It can track temperature to monitor dangerous conditions in areas such as chemical plants and coal mines. Anything that gives off a heat signature can be shown on these amazing images. This image shows field-unit geometries in front of the background of color-infrared aerial photographics.

Cartographic Animations

     Cartographic animations are an important way of displaying results and falls with geovisualization.  Having a time series of information can inform the viewer of things that aren't necessarily apparent when looking from image to image without the assistance of an animation. Trends become distinct as we see images before and after a single frame. This can even allow us to make predictions and forecasts based off of previous behavior. This animation is of Hurricane Andrew that struck in 1992. The animation shows the progression of the hurricane as it traveled across the state of Florida.

Dot Distribution Maps

     These types of maps are an easy way to depict density of whatever variable is being plotted. The visual clustering of dots shows a high density of the variable occurring while large spacing inbetween the dots shows low density values. This example shows earthquake locations for events between 1965 and 1995. The red dots are shallow earthquakes, the green are intermediate depth, and the blue and purple are deep.

Digital Raster Graphic (DRG)

     A DRG is a digital image resulting from scanning a paper USGS topographic map so that it could be used on a computer. The raster image usually includes the original border information (also known as the map collar). The map file is then UTM projected and georeferenced to the surface of the earth. These are commonly used in GIS applications, also. This particular example is a DRG of an area in West Virginia.

Public Land Survey System (PLSS)

     A PLSS is a reference scheme for recording property ownership by section, township, range, and aliquot parts in the United States. It is surveying method used historically over the largest fraction of the United States to survey and spatially identify land parcels before designation of eventual ownership, particularly for rural, wild or undeveloped land. The system divides up the land into relatively equal partition which is easier to manage. It also helped  to facilitate the urbanization of areas by using a square block system for the road design. the example shown is a portion of the Minnesota's statewide PLSS base map; this view is a small part of the 1:100,00 scale Worthington quadrangle. This example makes it very clear to see the different numbered sections showing which land parts belong to which section.