UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122"]], AUTHORITY["EPSG","4326"]] SRID values associated with spatial data can be used to constrain spatial operations — for instance, spatial operations cannot be performed between spatial objects with differing SRIDs in some systems, or trigger coordinate system transformations between spatial objects in others. See also Engineering datum Geodesy Geodetic datum Georeferencing Geographic coordinate systems Geographic information system (GIS). Grid reference List of National Coordinate Reference Systems References External links spatialreference.org – A website that defines spatial reference systems, in a variety of formats. OpenGIS Specifications (Standards) OpenGIS Simple Features Specification for CORBA (99-054) OpenGIS Simple Features Specification for OLE/COM (99-050) OpenGIS Simple Features Specification for SQL (99-054, 05-134, 06-104r3) OGR — library implementing relevant OGC standards EPSG Geodetic Parameter Registry - search engine for EPSG defined reference systems EPSG.io/ - Full text search indexing over 6000 coordinate systems Galdos Systems INdicio CRS Registry Geographic coordinate systems Geographic information systems Geodesy ISO/TC 211 Open Geospatial Consortium GIS file formats