Data creation

Geometry

The geometry for OS MasterMap Greenspace Layer is inherited directly from OS MasterMap Topography Layer.

Selections have been made to ensure that OS MasterMap Greenspace Layer is comprised of relevant polygons from the Topography Layer, with a green space focus. This green space determination comes from the Topography Layer attribution itself, and green space-relevant sites, some of which can also be found in the OS Open Greenspace product.

The Topographic area geometries and green space site layer attribution are combined in an automated process to produce a consistent layer of green space areas across urban Great Britain.

Attributes

The feature identifying attribution (TOID and Version) are taken directly from OS MasterMap Topography Layer.

Green space attribution is populated through overlaying green space sites onto OS MasterMap Topographic Area features. A subset of these green space sites is used to produce OS Open Greenspace.

Data completeness

Ordnance Survey is committed to maintaining its products to the highest levels of accuracy and currency. The initial capture of data for OS MasterMap Greenspace used our existing topographic databases and aerial imagery. As such, the quality of the data will be constrained to what can be achieved with this approach. For example, where an access into a site is obscured (for example, under trees) it will not be captured. In addition, the use of our existing databases to identify the location of sites of interest means that we cannot guarantee that all relevant sites will be included in the data. However, where we are informed and can verify that a feature is missing or inaccurately depicted in the dataset, we will make the necessary amendments to the dataset within six months of such verification. You can inform OS of any missing or inaccurately depicted feature in this product via the Error Reporting Tool on the OS Data Hub.

Positional accuracy

Since OS MasterMap Greenspace is a subset of topographic areas from OS MasterMap Topography Layer, it will inherit the positional accuracy from that product.

For a full explanation on OS MasterMap Topography Layer accuracies, please see the technical specification.

Coordinate reference systems

The Geography Markup Language (GML), ESRI Shapefile, and GeoPackage formats use the British National Grid (BNG) spatial reference system. BNG uses the OSGB36 geodetic datum and a single Transverse Mercator projection for the whole of Great Britain. Positions on this projection are described using easting and northing coordinates in units of metres.

Vector tile format is supplied in Web Mercator projection (EPSG:3857). Web Mercator projection uses WGS84 geodetic datum to render the vector tiles.

A guide to coordinate systems in Great Britain is available in additional resources under Coordinate systems in GB.

A general introductory guide to BNG is provided at:

http://www.ordnancesurvey.co.uk/resources/maps-and-geographic-resources/the-national-grid.html