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YOU ARE HERE: PLANNING AND COMMUNITY DEVELOPMENT > GIS > FREQUENTLY ASKED QUESTIONS |
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Frequently Asked Questions What is GIS? GIS is an acronym that stands for Geographic Information System. A GIS is an organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information. Geographic information systems contain information about the distribution of physical and human characteristics of places or areas, and are used in demography, town planning, natural resources management, engineering, education, government, business, marketing, logistics, distribution, and many other areas. Certain complex spatial operations are possible with a GIS that would be very difficult, time-consuming, or impractical otherwise. What is Planimetric Data? Planimetric data refers to 3-dimensional data for use in the Champaign County GIS. The current planimetric project includes the capture of road pavement centerlines, road pavement edges, water features, road bridges, and road intersection nodes.
The green lines in this image are road centerlines, and the pink lines represent road pavement edges. The planimetric data is overlaid with an orthophoto.
The image above is a 3-D view of downtown Champaign. The buildings are classified by color according to use, and height is determined by the number of stories. What is Metadata? Metadata—is data about data. Metadata documents the source, description, specifications, accuracy, time of acquisition, and quality of each data element. Thus, giving meaning, context, and organization to the data set. What is Orthophotography? Orthophotography combines the image characteristics of an aerial photograph with the geometric qualities of a map. Unlike a typical aerial photograph, distortions due to relief displacement (hills, stream valleys, buildings), camera lens, and aircraft altitude have been removed so that all ground features are shown in their correct ground positions. This makes a true image map possible and permits direct measurement of distances, areas, angles, and the detailed portions of ground features that are typically omitted or generalized on traditional maps. In a digital format, orthophotography fulfills a fundamental role as a geometrically accurate base map. Why were large X’s painted on roads all over the county? The process of creating orthophotos requires very precise ground control. To meet this requirement, large targets (see picture) in the shape of an X are literally painted on the ground. The targets are painted precisely over know surveyed points or they are re-located with Global Positioning System technology, (GPS). These targets show up on the aerial photos and are then used to control the accuracy of the photos by verifying that the digital image coordinates are very close to the known ground coordinates.
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