--- title: ISO 19136 — Geography Markup Language description: Explains GML 3.2.1 geometry, coordinates and CRS references, and distinguishes them from LongitudeOne's available spatial primitives. canonical_html: ./iso-19136.html canonical_markdown: ./iso-19136.md --- [View HTML version](./iso-19136.html) GML describes geographic features and their spatial and non-spatial properties in XML. Its geometry schemas provide an interchange representation; a PHP geometry classification is not itself a GML document or an XML schema. ## Normative source This reference examines **ISO 19136:2007**, *Geographic information — Geography Markup Language (GML)*, first edition, **September 2007** ([ISO catalogue][iso]). The accessible technical source is **OGC 07-036**, *OpenGIS Geography Markup Language (GML) Encoding Standard*, **3.2.1**, dated **2007-08-27** ([official PDF][gml]). OGC identifies GML 3.2 as ISO 19136:2007 in its [conformance test suite][suite]. All technical clause references below refer to the inspected OGC 07-036 text. The [OGC GML catalogue][catalogue] lists the corrected GML **3.2.2** document, **07-036r1**, separately. This page summarizes the base 3.2.1 text, without asserting corrected-edition requirements or conformance to them. ISO identifies **ISO 19136-1:2020** as the successor to the withdrawn 2007 edition; requirements of that successor are outside this reference's scope. The edition examined here provides a verified geometry reference. It does not establish that LongitudeOne implements or claims conformance to ISO 19136. ## Purpose and scope GML covers XML application schemas, geographic features, geometries, reference systems, topology, time and other geographic information (OGC 07-036, clause 1). The geometry subjects relevant to LongitudeOne's spatial primitives are: - geometry families and aggregates (clauses 10–11); - coordinate tuples and lists (10.1.4); - reference-system identification and coordinate dimensions (10.1.3.2). GML is broader than a geometry-only format. Its XML identities, property elements and application schemas are separate from geometry family names. ## Relevant requirements ### Geometry objects and families **Normative summary:** geometry types derive from `AbstractGeometryType`, and geometry elements belong to the `AbstractGeometry` substitution group directly or indirectly. Geometry elements have a `gml:id` identifier (10.1.3.1). Point, curve, surface and solid schemas are described in 10.3–10.6. Aggregates include `MultiGeometry`, `MultiPoint`, `MultiCurve` and `MultiSurface` (11.3). These XML structures must not be inferred solely from a PHP enum case. ### Coordinates and reference systems **Normative summaries:** - `srsName` references a CRS. When absent, the containing context supplies the CRS. `srsDimension` counts coordinate values per position, derives from the CRS and is omitted when `srsName` is omitted (10.1.3.2). - `pos` represents a direct position, with CRS information that can come from the containing geometry (10.1.4.1). - `posList` represents positions in one CRS. Its number of values equals the position count multiplied by the CRS dimension. Supplying `count` also requires `srsDimension` (10.1.4.2). - `Point` contains a single coordinate tuple. The older `coordinates` element is deprecated in favour of `pos` (10.3.1). **Informative explanation:** an integer SRID is not the same representation as the URI-valued `srsName`. Likewise, an XYM layout has three stored ordinates but does not by itself establish a three-axis CRS. A GML mapping needs an explicit interpretation of coordinates and their reference system. ### Conformance **Normative summary:** GML application schemas use the schema components from clauses 7–19 according to clause 21; profiles follow clause 20. Clause 2 defines conformance classes rather than requiring every application to implement all GML capabilities (2.1). Geometry names alone do not establish conformance. ## LongitudeOne support The assessed implementation is **Spatial Core 1.3.0**, revision `1289582288e8954243de5ccb1f28ab7e78f4e9a4`. It provides PHP enums and technical primitives, including geometry families and XY/XYZ/XYM/XYZM coordinate layouts. The support record describes that released package; it does not assign a GML support status to other libraries or DBMS integrations. | Feature | Implementation scope | Status | Limitations | Implementation decision | Extensions | Evidence | | --------------------------------------------- | -------------------- | ----------- | ------------------------- | ----------------------- | --------------- | ----------------------------- | | [Geometry classification][geometry-use] | Core 1.3.0 | Supported | PHP classification only | Geometry enum | None documented | [Enum][families] | | [Coordinate layouts][coordinate-use] | Core 1.3.0 | Supported | No GML/CRS mapping | Distinct Z and M | None documented | [Coordinate enum][dimensions] | | [GML geometry XML][geometry-use] | Core 1.3.0 | Unsupported | No XML representation API | Technical primitives | None documented | [Public API][core] | | [GML schemas and validation][conformance-use] | Core 1.3.0 | Unsupported | No schema validation API | Technical primitives | None documented | [Public API][core] | **LongitudeOne implementation decision:** enum membership describes a model classification. It does not supply concrete geometry objects, GML elements, `gml:id`, CRS URIs or XML schema validation. The supported primitive rows above are implementation capabilities, not claims of GML conformance. **Extensions:** none are documented for the assessed GML capabilities. SQL/MM layout modifiers and names in a PHP enum are not identified here as GML extensions. No blanket ISO 19136 conformance is claimed. ## Related references - [ISO reference overview](index.md) - [SQL/MM Spatial](iso-iec-13249-3.md) - [Spatial Core 1.x primitives](../../spatial-core/v1/geometry/index.md) - [Reference authoring contract](../../shared/spatial-reference-documentation-architecture.md) - [Official GML 3.2.1 schemas][schemas] [iso]: https://www.iso.org/standard/32554.html [gml]: https://docs.ogc.org/is/07-036/07-036.pdf [catalogue]: https://www.ogc.org/standards/gml/ [suite]: https://cite.ogc.org/teamengine/about/gml32/3.2/site/ [schemas]: https://schemas.opengis.net/gml/3.2.1/ [core]: https://github.com/longitude-one/spatial-core/blob/1289582288e8954243de5ccb1f28ab7e78f4e9a4/README.md [families]: https://github.com/longitude-one/spatial-core/blob/1289582288e8954243de5ccb1f28ab7e78f4e9a4/lib/Enum/GeometryTypeEnum.php [dimensions]: https://github.com/longitude-one/spatial-core/blob/1289582288e8954243de5ccb1f28ab7e78f4e9a4/lib/Enum/CoordinateDimensionEnum.php [geometry-use]: #geometry-objects-and-families [coordinate-use]: #coordinates-and-reference-systems [conformance-use]: #conformance