Geographic Information System GIS is a computer system capable of assembling, storing, analyzing, and displaying geographically referenced information. Locations of geographic features are stored in layers called coverages. Geographic features are represented in the coverages as polygons, lines, or points. Attributes of geographic features and related information are stored in files called tables.
Attribute tables contain one record for each feature in the coverage.
For example, in a coverage representing wells, the attribute table contains one record for each well. An attribute table may contain information such as well identification number, depth, and other construction data. Data tables may be independent of a coverage but, because GIS is a relational data base, can be linked to the attribute table using a common attribute, such as well identification number. For example, in a water-level data table, multiple records of historical water levels can be stored for each well. Because each of the multiple records contains the well identification number, which is the common variable, the well coverage attribute table can be related to the data table.