fgeometrycolumn

fgeometrycolumn is a reference to the field that stores the name of a geometry column within the PostGIS geometry metadata. In practice, this is usually written as f_geometry_column in PostGIS documentation and database catalogs. The term may appear without the underscore in older sources or code, but the concept remains the same: it identifies which column in a table contains geometric data.

In PostgreSQL databases with PostGIS enabled, geometry columns are tracked in a system catalog called geometry_columns. This metadata table (or view in modern installations) records information about each geometry-enabled column, including the table it belongs to and the specific column name. A typical set of fields includes f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, type, and srid. The f_geometry_column field stores the actual column name that holds geometry data for that table.

Usage and purpose: The f_geometry_column field enables tools and functions to discover and work with spatial data in a database. It supports compatibility with older workflows that required explicit registration of geometry columns. The AddGeometryColumn and DropGeometryColumn functions were historically used to register and remove geometry columns, ensuring the geometry_columns metadata stays in sync. Modern PostGIS deployments often rely on the presence of a true geometry type column, with geometry_columns providing a readable catalog of existing geometry columns for introspection and tooling.

Example: SELECT f_table_schema, f_table_name, f_geometry_column, type, srid FROM geometry_columns WHERE f_table_name = 'roads';

Notes: The geometry_columns metadata remains a standard reference in PostGIS, though newer workflows may rely more on direct column definitions. The f_geometry_column field is central to identifying where geometry data resides within each table.