Digimap: Boundary-Line

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Boundary-Line^™

Introduction

Boundary-Line is the key dataset of administrative and voting boundaries in Great Britain. It is a representation in computer-readable form of a specialist large-scale map. Real-world objects, which may be tangible (such as the mean high water mark) or intangible (such as a district boundary), are included.

Contents of Boundary-Line

Boundary-Line contains the following information:

civil parishes (England) and communities (Wales);
counties;
districts;
metropolitan districts;
electoral divisions (county and unitary);
European Electoral regions;
Greater London Authority;
London boroughs (including the county of the City of London);
Greater London Authority Assembly constituencies (the London Proportional Representation voting areas);
metropolitan districts;
parliamentary (Westminster) constituencies;
parliamentary (Scottish) constituencies and electoral regions;
unitary authorities;
wards (district, unitary, metropolitan and London borough);
Welsh Assembly constituencies and electoral regions;
extent of the realm (EOR) - either mean low water mark (England and Wales), mean low water springs mark (Scotland) or seaward boundary extensions;
mean high water mark (England and Wales) and/or mean high water springs mark (Scotland) (both are abbreviated to MHW in this user guide);
distinctive names;
census agency codes in England, Wales and Scotland for counties, unitary authorities, districts, wards and electoral divisions;
area measurements;
unique administrative unit, link and polygon identifiers;

Boundary-Line File Formats

The NTF files available for download are divided by area. There are individual NTF files for each County, Unitary authority and European Region of Great Britain. NTF files for each County and Unitary Authority contain all the boundaries for all the other datasets within them.

Extensive boundary sets that contain all features for a particular type of boundary such as Westminster Constituencies or Parishes are available as ESRI shapefiles or MapInfo MID/MIF files.

Accuracy and 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 on the source Ordnance Survey 1:10 000 Land-Plan. A consequence of this is Boundary-Line is superimposed upon boundaries in basic scales Land-Line data, variations in the two alignments will be seen.