# GML overview

## Simple Features – Level 1 <a href="#id-4.1-simple-features-level-1" id="id-4.1-simple-features-level-1"></a>

The Geography Markup Language (GML) data conforms to GML Simple Features Profile Level 1. In this release of the product, the only thing that does not conform to level 0 is the inspireId.

The geometries that we use are OGC ‘simple’: points, and line strings with linear interpolation.

## Schemas <a href="#id-4.2-schemas" id="id-4.2-schemas"></a>

XML schemas are used to define and validate the format and content of the GML. The GML 3.2.1 specification provides a set of schemas that define the GML feature constructs and geometric types. These are designed to be used as a basis for building application-specific schemas, which define the data content.

The Ordnance Survey application schema `waterNetwork.xsd`, which is referenced by the data, is available on our website. It imports the INSPIRE Hydrography networks application schema, which in turn imports the GML 3.2.1 schemas. These in turn import schemas produced by the W3C. The data contains elements and attributes from a range of namespaces:

#### The XML namespaces used by the application schema and their definitions:

<table data-full-width="true"><thead><tr><th width="498">Namespace Identifier</th><th width="181">Short Form Prefix</th><th>Application Schema</th></tr></thead><tbody><tr><td><code>http://namespaces.os.uk/mastermap/waterNetwork/1.0</code></td><td>water</td><td>OS MasterMap Water Network Layer</td></tr><tr><td><code>urn:x-inspire:specification:gmlas:HydroNetwork:3.0</code></td><td>hy-n</td><td>INSPIRE Hydrography networks</td></tr><tr><td><code>urn:x-inspire:specification:gmlas:Network:3.2</code></td><td>net</td><td>INSPIRE generic network</td></tr><tr><td><code>urn:x-inspire:specification:gmlas:BaseTypes:3.2</code></td><td>base</td><td>INSPIRE base types</td></tr><tr><td><code>http://www.opengis.net/gml/3.2</code></td><td>gml</td><td>OGC GML 3.2.1</td></tr><tr><td><code>http://www.w3.org/1999/xlink</code></td><td>xlink</td><td>W3C XML Linking</td></tr><tr><td><code>http://www.w3.org/2001/XMLSchema-instance</code></td><td>xsi</td><td>W3C XML Schema instance</td></tr></tbody></table>


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.os.uk/os-downloads/resources/product-resources/end-of-life-product-documentation/os-mastermap-water-network-layer/os-mastermap-water-network-layer-technical-specification/gml-overview.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.