# Data structure The data structure applies to the GML, ESRI shapefile and GeoPackage.\[KS1] ## UML diagram and table conventions The data structure is described in this section by means of unified modeling language (UML) class diagrams and accompanying tables containing text. The UML diagrams conform to the approach specified in ISO 19103 Conceptual schema. Colour conventions have been used in the diagrams and tables to distinguish the properties that have been added in this specification. In the UML diagrams, classes in the Ordnance Survey product specification are orange. All code lists are coloured blue. Therefore, the tables which follow in this Technical Specification use orange for a feature type and blue for a code list. ## Stereotypes The following stereotypes are used on UML elements: | Stereotype | UML element | Description | | ----------- | ----------- | -------------------------------------------------------------------------- | | FeatureType | Class | A spatial object type \[ISO 19136]. | | CodeList | Class | A controlled set of values for a free text data type that may be extended. | ## Formats OS OML is available in the following formats: • Vector: GML (Geography Markup Language) v.3.2.1 Simple Features and schema, which is zipped as a single file using gzip • Vector: ESRI shapefile, with each tile dataset zipped using gzip • Vector: GeoPackage, with a single zipped file for a national set (Great Britain) • Raster: GeoTIFF, compressed using LZW (Lempel-Ziv-Welch), is a TIFF file which has geographic (or cartographic) data embedded as tags within it. The geographic data can then be used to position the image in the correct location and with precise geometry on the screen of a geographic information display --- # 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/products/maps-and-imagery-portfolio/os-openmap-local/os-openmap-local-technical-specification/data-structure.md?ask= ``` 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.