Product purpose

OS MasterMap Topography Layer was initially developed in response to the need for a national topographic dataset that offers users a more sophisticated type of data that represents the world in a more realistic way and is more aligned to the increasing use and functionality of geographic information systems (GIS) and spatial database technology within organisations.

The product's primary purpose is to provide the most detailed topographic data available of the physical environment of Great Britain. OS MasterMap Topography Layer is regularly updated by ground and aerial survey to a regular schedule, and the data is captured and published to a consistently high standard.

Many users apply geographic products as a starting point to derive their own data, which can be time consuming and inefficient. This is particularly true where features in the data are amalgamations of more than one real-world feature, or even individual parts of a real-world feature. Where the feature represents a real-world feature that has an ‘area’, such as a building or a parcel of land, the feature is represented in the data as a polygon. This should provide opportunities for users to derive their data with greater efficiency and ease as features can be selected either singularly or in groups. The way, and, largely, the extent of a user’s ability to take advantage of the polygonised structure will depend on the systems in use in their organisation. However, most GIS have the necessary ‘data capture’ tools to analyse and interrogate the topography features.

OS MasterMap Topography Layer provides detailed attribution, through its descriptive terms, relating to the real-world object and the group of features it represents. This means certain types of analysis can be performed, without the user having to manually add their own attribution to the data. The themed attribution (see product themes for more information) also means the user can apply their own criteria to refine the data into groups of features that meet their own specific requirements. An example of this would be finding buildings of a certain size by using the calculated area provided as one of the attributes.

It is important for many applications of geographic information (GI) to be able to identify where changes have taken place and the history of a feature's changes. This is important because users may need to learn how the landscape has altered and reflect those changes in their own data. Ordnance Survey updates

OS MasterMap Topography Layer on a regular basis, and these changes are passed on to users through a dataset called change-only update (COU). COU supplies just the features that have changed since the last update or customer user order. This should normally result in much less data needing to be processed and uploaded to the user’s holdings upon the arrival of each update. This is, however, dependent on how frequently the COU data is applied. Furthermore, OS MasterMap Topography Layer is the first product from Ordnance Survey to introduce the concept of feature lifecycles and unique referencing. This makes it possible to relate change in the real world to features in the digital environment, and to identify and manage that change to OS MasterMap Topography Layer so that users can, if they wish, keep their own data holdings up to date. This will also enable the user to assess the consequences of feature changes. It may even be possible, depending on the systems used, for users to roll back their holdings of OS MasterMap Topography Layer to a specific point in time. However, Ordnance Survey does not supply previous versions of any feature or dataset.

Thematic maps

One of the most common uses for GI is to produce maps that are coloured to highlight a particular value or property that a real-world feature may have; these are often called thematic maps. An example is given in the image below. This image was created by grouping the calculated area value attribute of each unit on an industrial park into one of five categories. Each category is ‘themed’ with its own colour. The ranges and colours are shown in the legend. Most computer systems offer the ability for features to be assigned a colour or style based on the value of an attribute; OS MasterMap Topography Layer has both the structure and attribution to make it relatively quick to produce such thematic maps. The result is data that is easier to customise, easier to interpret and more eye-catching.

Thematic mapping with OS MasterMap Topography Layer.

Linking datasets

One common barrier to users is linking datasets together and sharing this data with other Ordnance Survey users, making greater use of their own data. To be able to link or ‘associate’ datasets together normally requires each dataset to have a common reference – one piece of information that is in all datasets. OS MasterMap Topography Layer can help to create links between users’ own datasets and

OS MasterMap features by using the TOID as a common reference. In this way, OS MasterMap Topography Layer provides a foundation dataset for a Digital National Framework that aims to help users of spatial data to derive more value by associating datasets together. Using a common reference can also provide such benefits to an organisation as removing ambiguity over a feature’s identity and allowing the faster retrieval of data when querying or analysing the data.