The vector product formats allow for the use of a variety of coordinate reference systems. At present, only British National Grid (BNG) is used in OS OML vector and raster data. 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 OML is derived from the latest versions of our OS MasterMap large-scale data and is refreshed every six months. More information about the OS MasterMap revision policy is available on the OS website.
During production, numerous checks are undertaken to ensure that the data supplied to customers is both accurate and complete. During digital manipulation and data creation, all data sources are checked for conformance to specification.
These quality checks take the form of:
• Visual checks by operators.
• Data testing against the product specification.
• Data testing on a selection of tiles from the full national set.
Geometry within OS OML has been generalised from Ordnance Survey large‑scale data. Map generalisation is the process of reducing the scale and complexity of map detail while maintaining the important elements and characteristics of the geometry.
Map generalisation comprises the following processes:
• Selection/omission: Some features that appear at larger scales are not selected at the smaller scales. For example, in the public amenities layer, individual features in close proximity can be grouped to a single point.
• Simplification: Simplification can take a number of forms in OS OML, including line simplification. For example, in the vector product, a stream can have many curves; these curves are represented by a number of data points which are filtered and will maintain the feature's shape.
• Exaggeration: This is the process whereby features that are small but are considered too important to a particular landscape to be omitted are enlarged. For example, isolated rural buildings are often enlarged to a minimum size rather than being omitted.
• Aggregation: Aggregation is the combining of a number of small features to make a larger one, such as buildings.
• Symbolisation: Features that are shown in detail in OS VectorMap Local may be collapsed to points within OS OML, which can then be symbolised if required. For example, railway stations and airports are depicted as point symbols.
• Displacement: This is the movement of the representation of a feature away from its ground position in order to maintain its prominence. There is very little displacement in OS OML, but in certain circumstances, some features may be moved away from adjacent detail if their representation would otherwise be lost.
In the vector product, features that cross tile edges are included in both tiles, represented as 'hairy' tiles. This facilitates the creation of a seamless dataset and avoids the creation of invalid geometries from arbitrarily cutting features along the tile border. All features have unique identifiers which can be used to remove the duplicated features across tile edges when stitching the tiles together. This supports the greater use of the data in large-scale analytical applications.
These identifiers will not be persisted or maintained between product releases.
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.
Coverage is Great Britain (i.e. England, Wales and Scotland).
55 tiles, each covering 100km x 100km, comprise the national set (Great Britain)
Each tile comprises up to 71 feature codes
Features that cross the tile edge are not split and are therefore duplicated within adjacent tiles (as explained in the edgematching section)
Tile sizes range from 10KB to approximately 200MB zipped
The file size of the national set (Great Britain) is 2.4GB zipped
55 tiles, each covering 100km x 100km, comprise the national set (Great Britain)
Each tile comprises a set of up to 20 shapefiles
Each shapefile holds a single feature type
Features that cross the tile edge are not split and are therefore duplicated within adjacent tiles (as explained in the edgematching section)
Tile sizes range from <17KB to approximately 181MB zipped
The data is not encrypted
The file size of the national set (Great Britain) is 2.4GB zipped
Only available as a national set (Great Britain)
Single file contains all the feature types
The data is not encrypted
The file size of the national set (Great Britain) is 3.8GB zipped
10 588 tiles, each covering 5km x 5km, comprise the national set (Great Britain)
GeoTIFF and compressed using LZW compression
Tile sizes range from 6KB to approximately 921MB zipped
The data is not encrypted
The file size of the national set (Great Britain) is 15GB zipped
OS OML is supplied to customers bi-annually in April and October, incorporating any updates made by the revision programme.
OS OML is supplied as an online download, which is available with no registration required. Data can be downloaded in various formats from the OS Data Hub.
OS OML can support a wide range of customer applications that utilise geographic information. The product is ideal for providing backdrop mapping on websites and displaying business locations on small-scale 'street level' maps.
OS OML has been designed for on-screen use, with generalised detail and an appropriate level of content that gives an uncluttered appearance.
The layered structure of the vectorised versions of OS OML enables you to display a map to show only the features you want to show (for example, roads, place names and buildings). In contrast, the rasterised version provides you with a pre-rendered and styled 'out of the box' backdrop mapping solution.
In both cases, you have the option to fade the map backdrop to ensure that your own or third-party overlaid data is clearly portrayed. This can be useful in cases where you need to draw attention to a specific point or feature.
Backdrop mapping is often used by public sector organisations to share information with the public, for example, providing the public with the location of GP surgeries or dentists within a set area.
OS OML lets you easily assess local sites of interest (for example, educational facilities), highlighting their location and context within an area. The backdrop style of the product gives great insight into an area while allowing the chosen data to stand out.
OS OML allows you to quickly identify hotspots in data (for example, recorded crime location or property prices) for representation within a local area. The muted colours of the detailed backdrop map give your information more prominence.
The local view of OS OML is ideal for creating a map of a street or neighbourhood to share the location of your business, complete with street and locality names to provide context.
OS OML features are generalised representations, but they still hold an instantly recognisable geometry to their associated real-world object. These objects include things like buildings, roads, railways and rivers. It also includes notable sites, such as schools, hospitals and transport hubs, with important buildings specifically identified within those sites. These notable sites are accompanied by non-topographic features, such as cartographic text and symbols.
This document contains additional theoretical information related to OS OpenMap – Local. All users will find the Product Information document useful and informative.
OS OpenMap – Local (OML) is the most detailed ‘street level’ open mapping product available and is designed to provide contextual mapping for your applications or web pages. It offers customers and OS Partners a clear contextual view of the world, whilst also enabling the undertaking of analytical activities.
In the example below, OS OML has been used as backdrop mapping to contextualise and provide a clear visual representation of a heat map for estimated house prices in an area:
OS OML data is available as either pre-styled static images (raster) or interactive vectorised features in a selection of pre-defined or customisable styles.
OS OML contains functional sites, greenspace, important buildings and Department for Transport (DfT) numbers in order to facilitate alignment with other OS products. When using OS OML for contextualised mapping, the nominal viewing scale is 1:10 000, with a recommended viewing scale range of 1:3 000 to 1:20 000.
The key features of the OS OML product are as follows:
• The vector data can be used for contextual mapping purposes and as a basemap with other third-party information.
• A full Great Britain set of data is available in Geography Markup Language (GML) v.3.2.1, ESRI shapefile, GeoPackage and GeoTIFF raster tiles.
• Road classifications are provided alongside comprehensive coverage of road names and numbers, in alignment with other OS products.
• The product contains important buildings, functional sites and greenspace.
• Generalised building geometries are derived from OS MasterMap large-scale data.
• Vector data map styling is highly customisable to suit your needs; premade stylesheets are also available for Ordnance Survey’s traditional styles.
• The product is updated twice a year.
• It is an OpenData product and is thus provided free at the point of use as a download through the OS Data Hub.
The vectorised format of the product consists of multiple layers of feature information which can be individually interrogated, displayed and styled to suit your needs. .
The rasterised layers provide pre-defined static contextual mapping that is designed to allow customers to overlay their own data clearly. More information on styling can be found in the product's Getting Started Guide, which is available from the .
