The geography spatial data type, geography, is implemented as a .NET common language runtime (CLR) data type in SQL Server. This type represents data in a round-earth coordinate system. The SQL Server geography data type stores ellipsoidal (round-earth) data, such as GPS latitude and longitude coordinates.
SQL Server supports a set of methods for the geography spatial data type. This includes methods on geography that are defined by the Open Geospatial Consortium (OGC) standard and a set of Microsoft extensions to that standard.
The error tolerance for the geography methods can be as large as 1.0e-7 * extents. The extents refer to the approximate maximal distance between points of the geographyobject.
Registering the geography Type
The geography type is predefined and available in each database. You can create table columns of type geography and operate on geography data in the same manner as you would use other system-supplied types. Can be used in persisted and non-persisted computed columns.
A. Showing how to add and query geography data
The following examples show how to add and query geography data. The first example creates a table with an identity column and a
GeogCol1. A third column renders the
geography column into its Open Geospatial Consortium (OGC) Well-Known Text (WKT) representation, and uses the
STAsText() method. Two rows are then inserted: one row contains a
LineString instance of
geography, and one row contains a
IF OBJECT_ID ( 'dbo.SpatialTable', 'U' ) IS NOT NULL DROP TABLE dbo.SpatialTable; GO CREATE TABLE SpatialTable ( id int IDENTITY (1,1), GeogCol1 geography, GeogCol2 AS GeogCol1.STAsText() ); GO INSERT INTO SpatialTable (GeogCol1) VALUES (geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656 )', 4326)); INSERT INTO SpatialTable (GeogCol1) VALUES (geography::STGeomFromText('POLYGON((-122.358 47.653 , -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))', 4326)); GO
B. Returning the intersection of two geography instances
The following example uses the
STIntersection() method to return the points where the two previously inserted
geography instances intersect.
DECLARE @geog1 geography; DECLARE @geog2 geography; DECLARE @result geography; SELECT @geog1 = GeogCol1 FROM SpatialTable WHERE id = 1; SELECT @geog2 = GeogCol1 FROM SpatialTable WHERE id = 2; SELECT @result = @geog1.STIntersection(@geog2); SELECT @result.STAsText();
C. Using geography in a computed column
The following example creates a table with a persisted computed column using a geography type.
IF OBJECT_ID ( 'dbo.SpatialTable', 'U' ) IS NOT NULL DROP TABLE dbo.SpatialTable; GO CREATE TABLE SpatialTable ( locationId int IDENTITY(1,1), location geography, deliveryArea as location.STBuffer(10) persisted )