Shapefile, TAB and GKPG

Source of Boundary-Line

The original data sources used for the creation of Boundary-Line was Ordnance Survey’s 1:10 000 scale boundary record sheets and OS Landplan digital data.

The data sources now used are Ordnance Survey’s Topographic Data for Natural Changes and Orders, Acts and Statutory Instruments (SIs).

Update currency

Boundary-Line is updated twice a year, in spring and autumn. The updated product is a full replacement for all the listed administrative and electoral boundaries. The represented boundaries and administrative unit names are defined and modified by Orders, Acts and Statutory Instruments (SIs). Changes that are operative from the first week of May in the current year of release will be included. Changes to Westminster constituencies that are effective from the date of the next general election will be included as separate files.

In exceptional circumstances due to processing or constitutional constraints, Orders, Acts and Statutory Instruments may be excluded until the next suitable release.

Superseded boundaries

Boundaries are no longer shown in Boundary-Line if they have been superseded at the time of the annual snapshot of boundaries that each release of Boundary-Line represents.

Government Statistical Service codes

Revisions to Government Statistical Service (GSS) codes are incorporated into Boundary-Line as soon as practicable after the information is made available to Ordnance Survey.

Tide lines and rivers

Additional coastline reconciliation with the OS Landplan product was introduced in May 2005. Changes to the Boundary-Line tide lines, plus natural and gradual changes to rivers and streams, have been implemented alongside the previous boundary/coast association to enhance the MHW FC0071.

All boundary alignment changes in Boundary-Line will be reported in the Release Note accompanying each release of Boundary-Line.

Resolution

The resolution of the coordinate system is 0.1 m. However, it is not possible to calculate meaningful accuracy limits for Boundary-Line data due to both the graphic nature and scale of the primary source 1:10 000 scale published mapping. Such mapping is subject to limited map generalisation, where an impression of the ground detail is made due to the complexity of the detail and importance of certain features such as roads. This means that boundary alignments are cartographically represented in areas where accurate positional representation would be impossible.

Boundary-Line is derived from the basic scale of 1:10 000. The relationship of boundaries to ground detail mirrors the accuracy achieved by mapping against OS VectorMap Local (1:10 000 scale) and, in certain cases, large-scale sources. A consequence of this is that if Boundary-Line is superimposed upon boundaries in OS MasterMap topographic data, variations in the two alignments will be seen.

Completeness

Completeness is a measure of the correspondence between the real world and the specified data content. During digitising, all Boundary-Line data is checked thoroughly against source documents to ensure as far as reasonably possible that no features have been omitted or misaligned.

Data properties

Boundary-Line is a structured link and polygon dataset. The data comprises three levels of features:

1. The administrative unit has attributes that include the administrative unit’s name and GSS code. The administrative unit feature is classified by means of a feature type. It also has explicit pointers to the polygons that define its area.

2. The polygon includes attributes that define its area value; it also has explicit pointers to the links that chains (or makes up) its edge and may have pointers to holes within the area.

3. The links have a geometry that defines their shape.

Administrative units, polygons and links are assigned unique identifiers for each release of Boundary-Line.

Data structure

Real-world administrative and voting units are modelled and named and have explicit pointers to the polygons that define their area of influence.

Each real-world administrative or electoral voting unit is classified by means of an area code. The polygons are classified indirectly by the administrative or electoral voting unit collection in which they appear. These polygons within the data model also have associated attributes which give the entities meaning, representing the geometric characteristic of an entity with items such as area or a unique identity.

Boundary links are classified indirectly by the polygon chains in which they appear.

Administrative or electoral voting units, polygons and links are assigned unique identifiers for each release of Boundary-Line.

Area features

Area features are polygons with attributes added.

Link features

Links represent all linear features; that is boundaries, extent of the realm (EOR) and mean high water (springs) mark (MHW). All links are broken when they intersect with one another. The first and last coordinate pairs in a link correspond exactly with the end coordinates of the adjoining link(s). Links may comprise up to several thousand line segments.

Coordinate system

The coordinate system is National Grid (NG). The National Grid coordinates are to a resolution of 0.1 metres. This is the resolution of the source data.