Geometrycolumns

Geometry_columns is a database metadata construct used by the PostGIS extension for PostgreSQL to catalog geometry columns stored in spatial tables. It provides a centralized, queryable view of all columns that contain geometry data, enabling GIS tools, client applications, and SQL functions to discover geometry-bearing columns without inspecting every table.

Structure and fields: In typical PostGIS installations, geometry_columns is a view with columns such as f_table_catalog, f_table_schema, f_table_name, f_geometry_column, type, coord_dimension, and srid. These fields identify the table and column that store geometry, the geometry type (for example POINT, LINESTRING, POLYGON), the coordinate dimension (2 or 3), and the spatial reference system identifier (SRID) used by that geometry.

Usage: A common query lists all geometry columns: SELECT f_table_schema, f_table_name, f_geometry_column, type, srid, coord_dimension FROM geometry_columns; The view is used by tools that need to know which columns hold geometry, such as export utilities, spatial indexes, or client GIS libraries.

Management: The view is maintained by PostGIS and is updated when geometry columns are created or modified via PostGIS operations. Older workflows used helper functions such as AddGeometryColumn, DropGeometryColumn, Populate_Geometry_Columns, and UpdateGeometrySRID to keep the metadata in sync. In modern workflows, geometry columns are typically created with standard SQL DDL and then metadata refreshed as needed.

Limitations: Geometry_columns reflects the current state of the database’s geometry metadata; it depends on the PostGIS extension being installed and properly initialized.