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Feature Collections

Following the OCG Features information model, the service API exposes PostGIS tables and views as feature collections.

The available feature collections can be listed. Each feature collection can report metadata about its definition, and can be queried to return datasets of features. It is also possible to query individual features in tables which have defined primary keys.

Expose Tables and Views as Feature Collections

pg_featureserv exposes all spatial tables and views which are visible in the database.

Spatial tables and views are those which:

  • include a geometry column;
  • declare a geometry type; and,
  • declare an SRID (spatial reference ID)

Visible tables and views are the available for access by virtue of by the database access permissions defined for the service database user. See the Security section for more information.

The service relies on the database catalog information to provide metadata about a table or view. The metadata includes:

  • The feature collection id is the schema-qualified name of the table or view
  • The feature collection description is provided by the comment on the table or view
  • The feature geometry is provided by the spatial column of the table or view
  • The identifier for features is provided by the primary key column for a table (if any)
  • The property names and types are provided by the non-spatial columsn of the table or view
  • The description for properties is provided by the comments on table/view columns

List Feature Collections

The path /collections returns a list of the feature collections available in the service as a JSON document.

Example

http://localhost:9000/collections

Each listed feature collection provides a name, title, description and extent. A set of links provide the URLs for accessing:

  • self - the feature collection metadata
  • alt - the feature collection metadata as an HTML view
  • items - the feature collection items

Describe Feature Collection metadata

The path /collections/{coll-name} returns a JSON object describing the metadata for a feature collection. The {coll-name} is the schema-qualified name of the database table or view backing the feature collection.

Example

http://localhost:9000/collections/ne.admin_0_countries

The response is a JSON document ontaining metadata about the collection, including:

  • The geometry column name
  • The geometry type
  • The geometry spatial reference code (SRID)
  • The extent of the feature collection (if available)
  • The column name providing the feature identifiers (if any)
  • A list of the properties and their JSON types

A set of links provide the URLs for accessing:

  • self - the feature collection metadata
  • alt - the feature collection metadata as an HTML view
  • items - the feature collection items