Spatial database

A spatial database is a general-purpose database (usually a relational database) that has been enhanced to include spatial data that represents objects defined in a geometric space, along with tools for querying and analyzing such data. Most spatial databases allow the representation of simple geometric objects such as points, lines and polygons. Some spatial databases handle more complex structures such as 3D objects, topological coverages, linear networks, and TINs (triangulated irregular network). While typical databases have developed to manage various numeric and character types of data, such databases require additional functionality to process spatial data types efficiently, and developers have often added geometry or feature data types. The Open Geospatial Consortium (OGC) developed the Simple Features specification (first released in 1997)^[1] and sets standards for adding spatial functionality to database systems.^[2] The SQL/MM Spatial ISO/IEC standard is a part the SQL/MM multimedia standard and extends the Simple Features standard with data types that support circular interpolations.^[3]

Geodatabase[]

A geodatabase (also geographical database and geospatial database) is a database of geographic data, such as countries, administrative divisions, cities, and related information. Such databases can be useful for websites that wish to identify the locations of their visitors for customization purposes.

Characteristics[]

Database systems use indexes to quickly look up values; however, this way of indexing data is not optimal for spatial queries. Instead, spatial databases use a spatial index to speed up database operations.

In addition to typical SQL queries such as SELECT statements, spatial databases can perform a wide variety of spatial operations. The following operations and many more are specified by the Open Geospatial Consortium standard:

Spatial Measurements: Computes line length, polygon area, the distance between geometries, etc.
Spatial Functions: Modify existing features to create new ones, for example by providing a buffer around them, intersecting features, etc.
Spatial Predicates: Allows true/false queries about spatial relationships between geometries. Examples include "do two polygons overlap" or 'is there a residence located within a mile of the area we are planning to build the landfill?' (see DE-9IM)
Geometry Constructors: Creates new geometries, usually by specifying the vertices (points or nodes) which define the shape.
Observer Functions: Queries which return specific information about a feature such as the location of the center of a circle.

Some databases support only simplified or modified sets of these operations, especially in cases of NoSQL systems like MongoDB and CouchDB.

Spatial index[]

Spatial indices are used by spatial databases (databases which store information related to objects in space) to optimize spatial queries. Conventional index types do not efficiently handle spatial queries such as how far two points differ, or whether points fall within a spatial area of interest. Common spatial index methods include:

Binary space partitioning (BSP-Tree): Subdividing space by hyperplanes.
Bounding volume hierarchy (BVH)
Geohash
Grid (spatial index)
HHCode
Hilbert R-tree
kd-tree
m-tree – an m-tree index can be used for the efficient resolution of similarity queries on complex objects as compared using an arbitrary metric.
Octree
PH-tree
Quadtree
R-tree: Typically the preferred method for indexing spatial data.^{[citation needed]} Objects (shapes, lines and points) are grouped using the minimum bounding rectangle (MBR). Objects are added to an MBR within the index that will lead to the smallest increase in its size.
R+ tree
R* tree
UB-tree
X-tree
Z-order (curve)

Spatial query[]

A spatial query is a special type of database query supported by spatial databases, including geodatabases. The queries differ from non-spatial SQL queries in several important ways. Two of the most important are that they allow for the use of geometry data types such as points, lines and polygons and that these queries consider the spatial relationship between these geometries.

The function names for queries differ across geodatabases. The following list contains commonly used functions built into PostGIS, a free geodatabase which is a PostgreSQL extension (the term 'geometry' refers to a point, line, box or other two or three dimensional shape):

Function prototype: functionName (parameter(s)) : return type

Distance(geometry, geometry) : number
Equals(geometry, geometry) : boolean
Disjoint(geometry, geometry) : boolean
Intersects(geometry, geometry) : boolean
Touches(geometry, geometry) : boolean
Crosses(geometry, geometry) : boolean
Overlaps(geometry, geometry) : boolean
Contains(geometry, geometry) : boolean
Length(geometry) : number
Area(geometry) : number
Centroid(geometry) : geometry