Spatial database

A spatial database is a database that is optimized to store and query data that is related to objects in space, including points, lines and polygons. While typical databases can understand various numeric and character types of data, additional functionality needs to be added for databases to process spatial data types. These are typically called geometry or feature. The Open Geospatial Consortium created the Simple Features specification and sets standards for adding spatial functionality to database systems.^[1]

Features of spatial databases

Database systems use indexes to quickly look up values and the way that most databases index 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 query types and many more are supported by the Open Geospatial Consortium:

Spatial Measurements: Finds the distance between points, polygon area, 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 such as 'is there a residence located within a mile of the area we are planning to build the landfill?' (see DE-9IM)
Constructor Functions: Creates new features with an SQL query specifying the vertices (points of nodes) which can make up lines. If the first and last vertex of a line are identical the feature can also be of the type polygon (a closed line).
Observer Functions: Queries which return specific information about a feature such as the location of the center of a circle

Not all spatial databases support these query types.

Spatial Index

Spatial indexes are used by spatial databases (databases which store information related to objects in space) to optimize spatial queries. Indexes used by non-spatial databases cannot effectively handle features such as how far two points differ and whether points fall within a spatial area of interest. Common spatial index methods include:

Grid (spatial index)
Z-order (curve)
Quadtree
Octree
UB-tree
R-tree: Typically the preferred method for indexing spatial data. 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
Hilbert R-tree
X-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.

Geography

A geodatabase is a database designed to store, query, and manipulate geographic information and spatial data of low dimensionality. It is a specialized type of spatial database often with optimizations for 2 and 3 dimensions, raster data and Euclidean distance.