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The core functionality added by a spatial extension to a database is one or more spatial datatypes, which allow for the storage of spatial data as attribute values in a table. [4] Most commonly, a single spatial value would be a geometric primitive (point, line, polygon, etc.) based on the vector data model.
For example, a data model for a city would include a list of data layers to be included (e.g., roads, buildings, parcels, zoning), with each being specified with the type of generic spatial data model being used (e.g. raster or vector), choices of parameters such as coordinate system, and its attribute columns.
There are also many different types of geodata, including vector files, raster files, geographic databases, web files, and multi-temporal data. Spatial data or spatial information is broader class of data whose geometry is relevant but it is not necessarily georeferenced , such as in computer-aided design (CAD), see geometric modeling .
A georelational data model is a geographic data model that represents geographic features as an interrelated set of spatial and attribute data. The georelational model was the dominant form of vector file format during the 1980s and 1990s, including the Esri coverage and Shapefile.
Inherently spatial formats were designed specifically for storing geographic data, while others are spatial extensions to formats designed for a more general use (e.g., GeoTIFF, spatial databases). Many data formats incorporate some form of data compression, especially raster files.
An object-based spatial database is a spatial database that stores the location as objects. The object-based spatial model treats the world as surface littered with recognizable objects (e.g. cities, rivers), which exist independent of their locations. Objects can be simple as polygons and lines, or be more complex to represent cities.
Attributes, characteristics of a feature other than location, often expressed as text or numbers; for example, the population of a city. [19] In geography, the levels of measurement developed by Stanley Smith Stevens (and further extended by others) is a common system for understanding and using attribute data.
GIS provide platforms for managing these data, computing spatial relationships such as distance, connectivity and directional relationships between spatial units, and visualizing both the raw data and spatial analytic results within a cartographic context. Subtypes include: