OS MasterMap^® Topography Layer - Latest news

Changes to access and presentation of Ordnance Survey control information:

Bench marks and triangulation points

After a public consultation in the spring of 2005, we have decided to remove the cartographic text associated with bench marks from the OS MasterMap Topography Layer. The topographic point (with height attribute) and cartographic symbol will remain.

Customers will start to see the changes in OS MasterMap Topography Layer from the next refresh of data on 4 April 2008

Surveying techniques have moved towards the Global Positioning System (GPS), and we are no longer maintaining traditional horizontal (triangulation stations) and vertical (bench marks) control points. As a result, the height information associated with these control points has become out of date.

We offer traditional control information to surveyors who do not use methods such as GPS. A frozen dataset of information is available at www.gps.gov.uk, as well as an expanding set of GPS based products and services.

For further information regarding this notice, please contact our Customer Service Centre on 023 8030 5030.

                
Before and after view in OS MasterMap Topography Layer of a bench mark

           
Before and after view in OS MasterMap Topography Layer of a trig pillar     

Tolerances

OS MasterMap Topography Layer is maintained using a spatial tolerance of 2 mm on line and area features within the Topography and landform structuring layers. The data has recently been through a quality improvement programme to ensure that this tolerance of 2 mm has been applied consistently.

For further information about tolerances please see the following webpage: http://www.ordnancesurvey.co.uk/oswebsite/products/osmastermap/faqs/topo028.html

Property extent polygon closing links

Property extent polygon closing links (PEPCLs, also known as inferred links) are used to create logical polygons to reflect that properties are separate entities; they do not represent legal boundaries. Following customer feedback, we have recently made changes to our capture specification to improve how PEPCLs are captured. Note that these changes impact on newly captured features, but retrospective action will not be applied.

In some open-plan estates it can be difficult to create PEPCLs as there is sometimes no logical placement. However, this can create large polygons as the front and back gardens of a number of houses then merge together. The specification has been amended so that if there is a gate, fence, hedge and so on that separates the back garden from the front, a general obstructing line will be added; otherwise, a PEPCL will be used. This should in most cases create a back garden for each property, in addition to a single open-plan front area, more accurately reflecting the real world.

Style

OS MasterMap offers customers many advantages over Land-Line^®; however, many customers have applications where they want to display a map that looks similar to Land-Line.  This may be because they want to display their own information against it, or that their own customers are more familiar with this depiction.

In response to customer feedback, we have created a style sheet for OS MasterMap that will replicate the Land-Line look and feel. The following link provides further information:

http://www.ordnancesurvey.co.uk/oswebsite/products/osmastermap/faqs/data009.html

Although it is not an exact replica of Land-Line, this style uses the features in OS MasterMap to create an appealing alternative.

We welcome feedback on this style - as well as feedback on what other 'default' styles you would like to see available.

Tidelines

Each mean high water (MHW) and mean low water (MLW) line has been represented twice in the data.  One line is used to form the edge of polygons; this line has themes of both water and land. The other line has a notional height on it and is in the themes of both water, and terrain and height. 

These lines are coincident; so many customers will not have noticed the presence of both lines. Some translators also remove one line during translation to avoid data duplication, so both lines may not be present in some customers' holdings.

In order to reduce data duplication and produce a cleaner product, one line will be removed from OS MasterMap. The line that is in the terrain and height theme will be removed. The line in the land theme will be retained as this is required in forming the edge of polygons.

We are currently assessing timescales for implementation and will publish more information as it becomes available.