multigeometry

MultiGeometry is a general term in geographic information systems (GIS) and computer graphics for a geometry that contains multiple component geometries, treated as a single object. It covers both specific multi-geometry types such as MultiPoint, MultiLineString, and MultiPolygon, and the more general GeometryCollection, which can hold any combination of geometry types.

A MultiGeometry stores an ordered collection of components; each component is itself a geometry with its own type and coordinates. All components share a common coordinate reference system. The concept allows complex features to be represented as one geometry entity, while preserving the distinct parts that make up the feature.

In terms of topology and validity, MultiPolygon components are typically required to be disjoint in their interiors within a single collection, though the exact constraints depend on the data model. GeometryCollection, by contrast, is more flexible and can contain overlapping or nested components, depending on the implementation and the governing standard.

Spatial operations can be applied to the collection as a whole or performed componentwise. Predicates such as intersects and contains may be evaluated against the aggregate geometry, while operations like union or difference can be executed by combining the results from individual components.

Usage scenarios include modeling features that consist of multiple parts, such as a city boundary with exclaves, a road network represented as several segments, or a building footprint that includes courtyards and holes. Representations vary by format: WKT uses GEOMETRYCOLLECTION for generic multi-geometries, while formats like GML and GeoJSON provide corresponding multi-geometry structures.

See also: GeometryCollection, MultiPoint, MultiLineString, MultiPolygon, WKT, GML, GeoJSON.