Contour data

GML

OS Terrain 50 contour layers are supplied in GML 3.2.1. It is recommended that you read this section in conjunction with the Open Geospatial Consortium (OGC) document, Geography Markup Language 3.2.1. An understanding of XML (Extensible Markup Language) and XML schemas is required. The XML specifications that GML is based on are available from the World Wide Web Consortium (W3C) website.

Data structure

The layer structure of the GML contour layers in the product is outlined in the following table.

Layer name	Layer description
<tile name>.gml	GML data file.
Metadata_<tile name>.xml	A metadata file for contour data, providing information on the flying date and so on.

Detailed GML model

UML diagram illustrating the data model and the relationships between the contour and grid GML supply of OS Terrain 50

Spot heights

These have been created by an automated process to select the highest mass point within every closed contour. If the point is the same height as the contour, it will be removed. It is possible that some spot heights could be lower than the surrounding contour due to genuine depressions. The z value is rounded to 0 decimal places.