Boundary-Line Product Information

This document contains additional theoretical information related to Boundary-Line. All users will find the Product Information document useful and informative.

Feature classes

Boundary-Line has three feature classes:

• Administrative units with attributes

• Polygon features with attributes

• Polyline features with attributes

Each feature has the following component:

• Feature attribute data

Each geometric feature has an additional component:

• Feature position

Feature position

The geometry of map features is defined in terms of coordinates. All coordinates used in Boundary-Line are based on the Ordnance Survey National Grid (NG) coordinate referencing system and are quoted to a 0.1m resolution. Despite this, Boundary-Line data can be no more accurate than its source, primarily the generalised 1:10 000 scale mapping.

There will be positional differences between the boundaries in Boundary-Line and Ordnance Survey large-scale topographic products. This is due to the large-scale products being surveyed to a higher degree of accuracy and associated to ground surface features, at scales such as 1:1 250 and 1:2 500.

Boundary-Line has been created as a more generalised set of administrative and electoral boundaries for the whole of Great Britain. It has been digitised against Ordnance Survey (generalised) 1:10 000 scale OS VectorMap Local mapping. The process of generalising for 1:10 000 scale mapping may have caused certain features to be moved from their true ground position for the purposes of map clarity. The result being that Boundary-Line and large-scale boundaries will not always be coincident.

Feature attribute data

An attribute is the descriptive characteristic of a feature, that is, a non-spatial element. In Ordnance Survey map data terms, an attribute can be a feature type (these are character codes), or a distinctive name, number or code, for example, Bassett Ward or 145.232 hectares.

Area codes

Each administrative unit is classified by means of an area code (AC). These area codes are allocated when each feature is initially interpreted and captured from source. This means that a county is distinguished from a ward by the area code allocated to it. The polygon features can be classified by tracing their relationships to administrative units. Consequently, links can be classified by tracing their relationships to polygons.

Other attributes

It is possible, with appropriate software, for you to add other names or values of your own choice as attributes of features.

Unique identifiers for link and polygon

There are two identifiers in Boundary-Line that help you identify features, and which are provided to create consistent references between successive releases of Boundary-Line data. They are unique within each feature type throughout the whole dataset and maintained through successive annual updates. These identifiers are never modified – only created or deleted. If a feature is deleted from the Boundary-Line database, then the identifier ceases to exist.

The two attributes are LINK_ID and POLYGON_ID.

Text

There is no direct cartographic text in Boundary-Line. Names, area values and GSS codes are held as attributes.