Product details

Generalisation

The detail within OS VectorMap Local has been generalised from Ordnance Survey large-scale data. Map generalisation is the process of reducing the scale and complexity of map detail whilst maintaining the important elements and characteristics of the location.

Map generalisation comprises the following processes:

• Selection / omission: Some features that appear at larger scales are not selected at smaller scales. For example, individual features in close proximity can be grouped to become a single point.

• Simplification: Simplification can take a number of forms in OS VectorMap Local. It can be line simplification, for example, in a vector product, a very winding stream could have the number of data points that represent it reduced.

• Exaggeration: The process by which small features that are too important to a particular landscape to be omitted are instead enlarged.

• Aggregation: Aggregation is where a number of small features (for example, buildings) are combined to make a single larger feature.

• Displacement: The movement of the representation of a feature away from its ground position in order to maintain its prominence.

Coverage

Coverage is Great Britain.

Coordinate reference system

The British National Grid (BNG) is used in OS VectorMap Local for all formats except vector tiles. The BNG spatial reference system 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.

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

Height datum

The BNG is a horizontal spatial reference system only; it does not include a vertical (height) reference system. In OS VectorMap Local, heights are given by the ‘height’ attribute in the ‘SpotHeight’ feature. The geometric attributes therefore contain horizontal geometry only.

Several orthometric height datums are used by Ordnance Survey to define vertical spatial reference systems. The most common of these is Ordnance Datum Newlyn (ODN), which is used throughout mainland Britain. The height information in OS VectorMap Local features does not specify which vertical reference system is used.

Currency

OS VectorMap Local is derived from the OS Large-Scale Topographic Database, which is the same data used to update OS large-scale product outputs such as OS MasterMap Topography Layer. This is the most up-to-date data available at OS.

Completeness

During production, numerous checks are undertaken to ensure that data supplied to customers is both accurate and complete. During digital manipulation, when creating the data, all sources of that data are checked for conformance to specification. These quality control checks take the form of:

• Visual checks by operators

• Automated tests on the national dataset

• Data testing against the product specification

• Selective testing carried out on a selection of tiles from a full national set

Product update schedule

OS VectorMap Local is supplied to customers quarterly in January, April, July and October, incorporating any updates made by the revision programme.