A spatial reference identifier (SRID) is a unique identifier associated with a specific coordinate system, tolerance, and resolution.
How the SRID is populated or what it represents can vary depending on what database you use to store your data. There are various recognized standard SRIDs, such as those defined by the European Petroleum Survey Group (EPSG). Some databases and spatial types, such as PostGIS geometry and geography in PostgreSQL or the geography type in Microsoft SQL Server, use a predefined subset of EPSG codes, and only spatial references with those SRIDs can be used. Others, such as the ST_Geometry type in Oracle, PostgreSQL, IBM Db2, and IBM Informix, can use spatial references that have SRIDs defined by Esri.
How SRIDs are used in ArcGIS
The following table lists what SRID is used in the target PostgreSQL, Oracle, or SQL Server database when importing or pasting spatial data. The words known or unknown indicate whether the spatial reference in the source data can be mapped to an existing spatial reference in the target database.
Source | Target | |||||
ST_Geometry | PostGIS Geography | PostGIS Geometry | Oracle SDO_Geometry | SQL Server Geometry | SQL Server Geography | |
Known EPSG code with an ST_Geometry, SDEBINARY, PostGIS geometry, PostGIS geography, SDO_Geometry, SQL Server geometry, or SQL Server geography column | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. This is only true for valid geography coordinate system as PostGIS geography does not support projected coordinate systems. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. |
Known EPSG code with custom tolerance and/or precision with an ST_Geometry or SDEBINARY column | An SRID greater than 300,000 is added to the geodatabase system table. | The EPSG code is used as the spatial reference ID and stored with the geometry. This is only true for valid geography coordinate system as PostGIS geography does not support projected coordinate systems. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. | The EPSG code is used as the spatial reference ID and stored with the geometry. This is true for geographic coordinate systems only, as projected coordinate systems are not supported. |
Known Esri coordinate system with an ST_Geometry, or SDEBINARY column | The Esri code is used for the ID and stored with the geometry. | An error is returned and the data cannot be imported. | The ID is set to –1. | The ID is null. | The Esri code is used for the ID and stored with the geometry. | Esri coordinate systems are used for projected coordinate systems. Since projected coordinate systems cannot be used with the SQL Server geography type, an error is returned and the data cannot be imported. |
Unknown coordinate system with an ST_Geometry, SDEBINARY, PostGIS geometry, SDO_Geometry, or SQL Server geometry column | An SRID greater than 300,000 is added to the geodatabase system table. | An error is returned and the data cannot be imported. | The ID is set to –1. | The ID is null. | The ID is set to 0. | An error is returned and the data cannot be imported. |
Custom Oracle coordinate system with an SDO_Geometry column | An SRID greater than 300,000 is added to the geodatabase system table. | An error is returned and the data cannot be imported. | The ID is set to –1. | The custom Oracle ID is used if it is set in the source. If not set, the SRID is set to null in the target database. | The ID is set to 0. | An error is returned and the data cannot be imported. |
Custom coordinate system with a PostGIS geometry column | An SRID greater than 300,000 is added to the geodatabase system table. | The custom PostGIS ID is used, if it is set in the source. If not set, an error is returned and the data cannot be imported. | The custom PostGIS ID is used, if it is set in the source. If not set, the ID is set to –1 in the target database. | The ID is null. | The ID is set to 0. | An error is returned and the data cannot be imported. |
When pasting or importing data to a Db2 or Informix database, ArcGIS also checks the spatial reference table for a match; if one is not found, a new record with the new information is added to the spatial references table. See your IBM documentation for more information about the IDs used.