Spatial Operations and Map Operations
Layer Algebra; Map Algebra; Theme Algebra
Map operations refer to the operations that an end user performs on maps stored in a database. Map information is stored according to themes (for instance, cities, roads, or population), sometimes called layers in the GIS terminology. The maps considered here are stored in a vector format – as opposed to a raster format such as a grid of pixels – and can be 1 dimensional (e.g., a network of roads for a navigation system), 2 dimensional (e.g., a map of land-use for regional planning activities), or 2.5 dimensional if the elevation at certain locations is considered (for instance, the height of a building in an architecture project). A map is made of what is often called geographic objects. A geographic object (for instance, a city) has two parts, an alphanumeric one (e.g., its name and population) and a spatial one (e.g., a polygon), usually called spatial object. The alphanumeric attributes of a geographic object constitute...
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