Overview
ISO 19125-1:2004 - "Geographic information - Simple feature access - Part 1: Common architecture" defines a platform-neutral architecture for simple feature geometry used in GIS and spatial databases. The standard specifies a Geometry object model (using UML), canonical names and geometric definitions for geometry Types (Point, Curve, Surface, GeometryCollection and their Multi* collections), and canonical text/binary representations. It standardizes key concepts such as Spatial Reference Systems (SRID), envelopes, boundaries and well-known encodings, while intentionally not prescribing how geometry Types are added, stored or maintained internally.
Key topics and technical requirements
- Geometry object model: A hierarchical, UML-described model with a root abstract Geometry class and concrete subclasses for 0-, 1- and 2-dimensional geometries (Point, LineString/Curve, Polygon/Surface) and collections (MultiPoint, MultiLineString, MultiPolygon, MultiCurve, MultiSurface).
- Attribute and method definitions: Standardized geometry methods include Dimension(), GeometryType(), SRID(), Envelope(), AsText(), AsBinary(), IsEmpty(), IsSimple(), Boundary() - useful for consistent API behavior across implementations.
- Well-Known representations: Defines Well-Known Text (WKT) and Well-Known Binary (WKB) formats for geometry, and WKT for spatial reference systems - enabling interchange of geometry across systems.
- Spatial reference handling: Each geometry is associated with a Spatial Reference System Identifier (SRID); ISO 19125-1 references ISO 19111 for coordinate referencing.
- Interoperability constraints: The standard standardizes names and geometric semantics but explicitly does not mandate internal storage, user-defined type mechanisms, or type-management mechanisms.
- Conformance: Implementations conform by meeting test suites specified in other parts of ISO 19125 (e.g., the SQL option in Part 2).
Applications and users
ISO 19125-1 is essential for:
- GIS software developers and spatial database vendors implementing geometry APIs and storage engines.
- Spatial data integrators and architects ensuring interoperability between mapping systems, web services and spatial SQL engines.
- Standards and QA teams validating conformance of spatial formats (WKT/WKB) and SRID usage.
- Developers implementing spatial functions (envelope, boundary, spatial relations) consistent with other ISO geomatics standards.
Practical benefits include predictable geometry behavior, portable WKT/WKB exchange, consistent SRID usage, and easier integration between GIS clients, servers, and spatial databases.
Related standards
- ISO 19125-2 (Simple feature access - SQL option)
- ISO 19107 (Spatial schema) - mapping provided in Annex A
- ISO 19111 (Spatial referencing by coordinates)
Keywords: ISO 19125-1:2004, simple feature access, geometry object model, WKT, WKB, SRID, spatial interoperability, MultiPolygon, Envelope, GeometryType.
