What is a GIS Shapefile?

A GIS shapefile is a file format used for storing geographic information data in GIS computer programs and databases, such as ArcGIS and ArcCatalog. The file extension for shapefiles is .shp. It is a vector data format, meaning that the geometric data is stored in vector coordinates. GIS shapefiles do not store topographical information, but are useful for storing geographical data, such as the locations of buildings and streets.

Point, line, and area data can all be stored in a GIS shapefile. Each piece of information is stored as a separate entity in the file, and these are called features. A point feature displays as a small dot on the map, and is used to store information like the locations of buildings or trees. Line features display as continuous lines and represent physical features, such as roads and rivers. Area features are flat, solid-colored polygons, which can be used to represent information, like census blocks or city zoning areas.

In addition to the vector data that displays on a map, a GIS shapefile can also store attribute information. This is stored in a database table, and all records in the table are associated with features on the map. An attribute table lists the vector coordinates for each feature, but it can also be used to store other information about them, such as the names of streets or the population of census blocks.

Shapefiles can be manipulated or converted to other data types in a variety of ways. Since the information is stored in vector coordinates, it is relatively simple to add features to a GIS shapefile. The size or attributes of existing features in a shapefile may also be edited. The data from two or more shapefiles can be combined, or the information in an attribute table may be linked to the table of another GIS file. Shapefiles may also be converted to a GIS raster file type, if more complex editing or statistical analysis is needed.

In comparison to other file types often used to store geographical data, GIS shapefiles are generally smaller files that can be created and edited more quickly. The simpler data form of a GIS shapefile, however, also restricts the types of editing that can be performed on the file, and makes it unsuitable for storing topographical data. Shapefiles are often used in conjunction with other types of files on the same map to perform complex geographical analyses.