Spatial data are the lifeblood of an emerging and exciting computer mapping technology know as geographic information systems or GIS. The GIS stores and manages the data not as a map but as a series of layers or, as they are sometimes called, themes. The examples of geographic data cited above are the layers or themes.
Within a GIS, attributes are stored with the geographic data. Attributes are simply the information that we know about the geographic data. For example, for a roads data layer, the attributes may include the road name, highway number, speed limit, paving material, maintenance history, or any other information related to the management or use of this particular layer. The GIS automatically calculates measurement information, such as the length of a road segment or the area of a land parcel. Take a look at visual description of GIS data.
The Accessing Spatial Data tutorial includes a section that defines GIS technology and describes typical GIS applications.
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