Geo-Spatial Index

Geo-Spatial Index

A geo-spatial index is a special form of spatial index which is based upon earth mapping coordinates in fractions of degrees. A geo-spatial index can only be constructed over a pair of numeric fields containing geo-spatial coordinates. One value must be identified as containing the longitude, and one value must be defined as containing the latitude. A geo-spatial index can be thought of as a distorted flat map similar to ones you may have seen in the past. The cells or rectangles used to partition the map are uniform, but the area near the poles is much larger than it would appear on a globe.

The grid is defined by a base (X,Y) coordinate pair, a width and height in fractional degrees for each cell within the grid, and the number of cells in each direction. Items that fall outside the grid may be included within the slot corresponding to the nearest cell, included in a special overflow slot, or discarded from the index.

Geo-Spatial indexes are defined by the following properties:

Property	Description
Index Name	Name assigned to the index.
Resource ID	Unique id assigned to the index.
Index Rules	Determines what part of the data an index is to be created over.
Long Min Coord	Smallest longitudinal coordinate mapped by the grid.
Long Cell Distance	Longitudinal distance in fractional degrees mapped by an individual grid cell.
E-W Cell Count	Number of cells in a single east-west row of the grid.
Lat Min Coord	Smallest latitudinal coordinate mapped by the grid.
Lat Cell Distance	Latitudinal distance in fractional degrees mapped by an individual grid cell.
N-S Cell Count	Number of cells in a single north-south column of the grid.
Decimal Places	Implied decimal places for geo-spatial coordinates.
Boundary Flag	Defines how values that fall outside of the base values are handled.
Weight	Applied to results returned using this index.