Basic GIS Jargon:

The geographic scope is the extent of the geographic area that for which you want coverage. For example, if you are doing research on parks in New Haven county, your geographic scope would extent to the boundaries of New Haven county.

Geographic units may only apply for certain types of data. For example, is you need Census data for New Haven county, the data could be divided up by towns, census tracts, block groups, or blocks. These would be your different types of geographic units and one may be more appropriate than anohter depending on your scope and the detail level of analysis required for your research.

Scale is similar to geographic units in that as scale varies, a corresponding level of detail will vary for geographic features. For example, a transportation layer derived from a 1:100,000 scale map may only contain interstates and highways, where as a transportation layer derived from a 1:24,000 scale map would probably contain detailed neighborhood roads and foot paths.

Thematic types of data refers to the types of geographic feature(s) needed for your research that can be grouped into thematic categories. Generally, most GIS data sets fall under one of the following categories: transportation, hydrology, political boundaries, hypsography (elevation), Census boundaries, and land use/ land cover.

Projection refers to how a map is projected from the round shape of the earth into a flat, 2-dimensional model. There are many types of map projections and one may be more appropriate than another depending on the type of analysis you want to do. For example, if you want to measure distances from New Haven, CT to several different cities around the world, you may want to use a azmuthal equidistant projection to preserve distance and direction more acurately. However, if you wanted visualize the comparison of vegetated land cover in different countries, you may want to use an equal area map projection to preserve area more acurately. Scale and scope also may play a factor in chosing the appropriate projection. If your scope covers the town of New Haven and you want to perform analysis that requires acurate measurements, you may want to use a Universal Transverse Mercator projection that is more acurate for very specific areas of the earth. However, if your scope covers a the whole Western Hemisphere, a UTM projection would greatly distort the features of the map outside the specified UTM zone- a plain Mercator projection may be more appropriate in this case.

Coordinate system refers to how the surface of the earth is broken up into equal units of measurement and what those measuring units are. Coordinate systems are closely related to projections and often the two come together as one standard sytem. For example, a UTM projection contains a coordinate system that breaks the earth into 60 zones measuered in meters. Another common coordinate systems include State Plane, which is generally measured in feet, but can also be in meters and only covers the United State (each state generally has one or more zones for this coordinate system). One more common coordinate system is latitude and longitude, which are usually expressed in degrees, minutes, and seconds or decimal degrees. This coordinate system covers the whole earth.

Visit the AGI GIS Dictionary site to find out more about GIS terminology.


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Last update: January 13, 2003 9:16
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