Boundary-Line Guidance Notes



Contents



Introduction

Boundary-Line is an Ordnance Survey dataset which provides administrative and electoral boundaries and their names for England, Scotland and Wales. Boundary-Line represents a full hierarchy of boundaries and 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.

The data was initially digitised from Ordnance Survey’s boundary record sheets at 1:10 000 scale (or, in some cases, at 1:10 560 scale). The 1:10 000 scale published mapping has being progressively withdrawn as it is replaced by Landplan®. Boundary-Line now uses this as the source document, occasionally mapped against large scale sources.

The census agency codes are supplied by Office of National Statistics (ONS) and General Registers of Scotland (GROS). Appropriate GIS software is needed to use the data for your intended application.

Boundary-Line comes in NTF, MID/MIF and Shapefile formats.



Contents of Boundary-Line

Features available in Boundary-Line

A list of the features within Boundary-Line includes:

File Structure and Sublevels

The data is supplied as named files. The named files include all of the other relevant sub-levels of electoral boundaries that belong under that high level administration; these are:

Named file type Possible sub-level of boundaries within the named file
County The named county, district, district ward, civil parish, county electoral division (ED).
Unitary authority The named unitary authority, unitary authority ward or unitary authority ED as appropriate, civil parish where appropriate, together with community in Wales.
Metropolitan district The named metropolitan district, metropolitan district ward, civil parish where appropriate.
Greater London Authority The Greater London Authority, Greater London Authority Assembly constituency, London borough, London borough ward.
Scottish parliamentary electoral region The named Scottish parliamentary electoral region, Scottish parliamentary constituency.
Welsh assembly electoral region The named Welsh Assembly electoral region, Welsh Assembly constituency.
Westminster constituency The named Westminster constituency.
European region The named European region.

The following represents the named files contained in Boundary-Line NTF May 2006 specification:

As a consequence of the named file supply, all coordinates in the supplied data file are full Ordnance Survey National Grid coordinates, as there is no concept of local origin.



Relationships of Administrative Areas

A district is a division of a county; a civil parish is a division of a district. A county is divided for voting purposes into electoral divisions (EDs) and a district is divided for voting purposes into district wards.

With the introduction of unitary authorities, there are now two- and three-tier local government hierarchies. The three-tier system remains unchanged; the two-tier system has unitary authorities replacing the county and district levels of administration. Unitary authorities may be divided into civil parishes or communities (except in Scotland); and unitary authority wards or unitary authority EDs for voting purposes. In Wales the voting area is the unitary authority ED; in Scotland it is the unitary authority ward, and in England it is the unitary authority ward (except in the Isle of Wight, where it is the unitary authority ED).

England also has metropolitan districts; these have no county administration. These districts are divided for voting purposes into metropolitan district wards.

With the introduction of the regional government for London, in this document called the Greater London Authority; the proportional representation voting area for this new administration is the Greater London Authority Assembly constituency. The existing London borough structure also has a relationship with the new Greater London Authority and each London borough is divided for voting purposes into London borough wards.

Scotland is divided into parliamentary constituencies for voting purposes; to elect members (MSPs) to the Scottish Parliament the Scottish parliamentary electoral region is a grouping of Scottish parliamentary constituencies.

Wales is divided into assembly constituencies for voting purposes; to elect members (AMs) to the Welsh Assembly. The Welsh Assembly electoral region is a grouping of Welsh Assembly constituencies.

Great Britain is divided into European regions (Scotland, Wales and nine English regions) for voting purposes to elect members (MEPs) to the European parliament.

England, Scotland and Wales are divided into parliamentary constituencies for voting purposes to elect members (MPs) to the Westminster parliament. Parliamentary constituencies are made up of combinations of Wards (or Electoral Divisions in Wales).

Nested and Layered Data Formats

Boundary-Line data is output in two structures:

NOTE: See chapter 3 of the Ordnance Survey Boundary-Line User Guide for diagrams and further information on how the different administrative areas relate to one another. The guides for all Ordnance Survey products can be found here: Download User Guides



Boundary-Line Principles and Features

The following explains the representation of features in Boundary-Line and describes various definitions and exceptions.

Administrative area

A term used by Ordnance Survey to refer to all public administrative areas. For the Boundary-Line dataset the following are included under this term:

Area values

Area values exist for every polygon in Boundary-Line, area values are quoted to the current Department for Communities and Local Government (DCLG) specification of 0.001 hectare. The value is subject to the inherited accuracies of the generalised 1:10 000 scale published mapping used as the source for Boundary-Line.

Boundary

A boundary is the limit of a predetermined and established area whose limit is determined by one or more lines. In Boundary-Line specifically, an administrative unit boundary, for example, a county area boundary.

Ceremonial counties

A ceremonial county is an area that has an appointed Lord Lieutenant and High Sheriff. Ceremonial counties are not explicitly represented in Boundary-Line.

Detached parts

The description Detached, (Det), only applies to portions of local government or parliamentary constituency areas which are separated from the main area, being completely surrounded by other local government or parliamentary constituency areas and not connected by direct access on the ground.

The description will not be applied to islands or parts of islands in the sea.

Detached parts have the same AI attribute (and census agency code where applicable) as the main area. Where there is more than one detached part they are numbered consecutively within the name, for example, MILTON CP (Det No 1).

Divorcement

Part of a boundary separated from another, originally on the same alignment. Divorcements are created by the revision of one boundary and not the other.

For example, the unitary boundary between Vale of Glamorgan and Cardiff has been realigned, whilst the parliamentary (Westminster) constituency boundary has remained in its original position. It is likely that the parliamentary (Westminster) constituency boundary will also be realigned at some time in the future.

Effective date

A future event of unknown date, for example, the next general election, at which time the changes specified in an Act, Order or Statutory Instrument will come into operation. This term is solely applied to parliamentary (Westminster) and European region boundaries. Boundary changes are not incorporated into Boundary-Line unless they have become operative at the time of the annual snapshot of boundaries that each release of Boundary-Line represents. Because of this, parliamentary constituencies and European regions in Boundary-Line are normally those in which the MPs and MEPs are or were sitting at the time of the annual snapshot of boundaries that each release of Boundary-Line represents.

For example, the new parliamentary constituency boundaries which became effective at the time of the June 2001 general election were first represented in the autumn 2001 Boundary-Line release.

Exception areas

The following are specific exceptions to the normal rules:

Honorary titles

Honorary titles granted to local government areas, such as city, borough and town, are not included in Boundary-Line.

National boundaries

The boundaries between England and Wales and England and Scotland are treated as county boundaries in Boundary Line.

Census agency codes

These codes are a unique system of referencing for administrative units.

The following types of unit are coded in Boundary-Line where they have been made available: counties, districts, metropolitan districts, London boroughs, unitary authorities, district wards, unitary authority wards and unitary authority EDs. The codes are allocated by the Office of National Statistics (ONS) for England and Wales and by the General Register Office for Scotland (GROS) for Scottish areas.

NOTES: The codes for Scotland were included for the first time in the 1997 release of Boundary-Line. The NTF OP record has a maximum of seven characters for the census codes. In three-tier local government hierarchy areas, the format of the codes is a combination of two digits for county and two letters each for district and ward, in the form CCDDWW (see the following example codes) or CCDDPAR for Parish census agency code.

Example codes for typical wards in Cheshire

13UBGU (College ward)
13UHGY (Helsby ward)
13UDGH (Birchin ward).
The code for a county consists of the first two characters, followed by four spaces.

Example code for a county

13 (Cheshire)
The code for a district consists of the first four characters, followed by two spaces:

Example code for a typical district

13UB (13 = Cheshire county and UB = Chester district)
In two-tier local government hierarchy areas, the format of the codes is four letters, followed by two spaces, where the first two letters represent the unitary authority, and the second two, the ward.

Example code for a sample ward in a unitary authority

ETMA (ET = Halton and MA = Halton Brook ward)
The code for a unitary authority area consists of the first two characters, followed by four spaces.

Example code for a unitary authority

NJ (Sir y Fflint - Flintshire)
Any OP code is set at 999999 when the information is not available to Ordnance Survey.
The code is blank when the administrative unit does not have a code.

Operative dates
This is a calendar date, given in an Order, Act or Statutory Instrument, on which the specified boundary changes will come into operation. Dates given may be up to four years after the publication of the Order, Act or Statutory Instrument and may apply to any type of boundary other than parliamentary or European regions. Each release of Boundary-Line represents boundaries (as defined and modified by Orders, Acts and Statutory Instruments where available to Ordnance Survey) as at a date that falls, typically, during the first week of the preceding May. Boundaries having an operative date that has not yet been reached by this date are not represented in that release of Boundary-Line.

Order, Act or Statutory Instrument
A document signed by the relevant Secretary of State or a local authority letter describing and giving legal authority for boundary changes. Other Acts and Orders can effect the addition of new boundary information, for example, seaward extensions and harbour acts.

Superseded date
The last date on which a boundary was current. Where an effective date applies, the superseded date will be the day before the next dissolution of Parliament, or the day before the next European Assembly election in the United Kingdom. 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.

Survey change
When changes occur to tide lines, rivers or streams caused by natural and gradual forces, any boundaries that are linked to these altered features will move with them. When the movement of a boundary, MHW or EOR alignment in Boundary-Line reflects such changes, this will be noted in the Update notes that accompany each release of Boundary-Line.

Un-annexed areas

This is an area within the realm which is not included in all the relevant administrative units. The area will remain un-annexed until further legislation changes its situation and the polygon represents a hole in that level of administration.

Unitary authorities

Unitary authorities and counties effectively create a contiguous layer of administrative units throughout the whole of Great Britain.



The Coastline and Associated Items

Extent of the realm (EOR)

The external bounding line of the Boundary-Line dataset is the extent of the realm. This means the boundary extent is digitised on the alignment of the mean low water springs (MLWS) for the seaward extent. Boundary-Line does not contain a separate MLWS only FC0071 mean high water (MHW).

NOTE: To display the EOR both mean high water (MHW) and another type of boundary, for example, European electoral region or Westminster constituency, need to be displayed together.

The Territorial Waters Jurisdiction Act 1878 and the Territorial Waters Order in Council 1964 confirm that the extent of the realm of Great Britain as used by Ordnance Survey is properly shown to the limit of mean low water for the time being, except where extended by Parliament.

This means that the extent of realm will be:

Foreshore

The foreshore is taken to be the area of land between mean high water (springs) mark and the extent of the realm which will include:

Mean high water (springs) mark is represented in Boundary-Line by a continuous link feature with feature code 0071. Mean low water (springs) mark is not shown, although it is generally coincident with the EOR. The area of non-inland is referenced within each administrative unit using the NA attribute.

Islands and rocks in the sea

The following rules govern the representation in Boundary-Line of offshore islands and rocks in the sea:

Offshore islands or rocks will not be shown if they are:

If an offshore island or rock is shown, it will be contained within all the relevant administrative unit collections.

Mean high water (springs)

The mean high water (springs) mark is shown to NTL (normal tidal limit). Areas of salt marsh, mud flats and so on, often have very complicated tide lines. For ease of digitising and to reduce data volumes, mean high water may be generalised in these areas (not Scotland).

Mean high water (springs) mark is represented in Boundary-Line by a continuous link feature with feature code 0071.

Mean high water (springs) mark is subject to continuous change but the captured alignment of a tide line is a snapshot on one day. It is not practical to revise tide lines very frequently.

Mean low water (springs)

Mean low water (springs) mark is shown as the extent of the realm, except when contained within a seaward extension, when it is then omitted.

Banks of sand, mud, shingle or rock separated from the main line of mean low water (springs), and covered at high tide, are not shown. When there are large areas of these banks separated from the main foreshore by narrow channels, the channels are ignored and the whole bounded by mean low water (springs).

The extension of the line of mean low water (springs) into a channel above Point B becomes edge of channel and is not shown. Mean low water (springs) mark, and hence EOR is subject to continuous change but the captured alignment of a tide line is a snapshot on one day. It is not practical to revise tide lines very frequently.

Normal tidal limit (NTL)

The point at which the level of a river or stream ceases to be affected by the tidal flow. This point is often an artificial barrier such as a lock or weir.

Pier

A pier under which water flows is not normally considered to be within the realm. There are some cases, however, where a structure has specifically been included within the realm by Act or Order, in which case mean high water springs) mark and EOR is shown around the limits of the structure.

Point B

This is the intangible line across a channel where the level of the river meets the level of the sea at low water. (see Figure 3.5a in the User Guide)

Within large channels or estuaries Point B is defined on the source documents for Boundary-Line, and is therefore shown as EOR.

In small channels, Point B is not shown on the source documents, so is assumed to be along the general line of low water and is shown as EOR.

Seaward extensions

These are artificial extensions to the realm that have been made by Act of Parliament. They extend the local government and parliamentary areas seaward of mean low water (springs) mark.

Structures in the sea

Breakwaters are structures of wood, stone, metal or other material built to break the force of waves. They can be separate from, or joined to, the mainland. If joined, they are generally included in the local government and parliamentary areas. If separate, they are not part of the local government and parliamentary area unless they are placed therein by legislation of some kind, for example, Plymouth breakwater is included in the local government area whilst the centre portion of the Portland Harbour breakwater is not.

Permanent structures in the sea, such as the forts in the Solent off Portsmouth Harbour, are usually included in local government and parliamentary areas.



Technical Information

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.

Census agency codes

Revisions to census agency codes are incorporated into Boundary-Line as soon as practicable after the information is made available to Ordnance Survey.

Tide lines and rivers

Introduced in May 2005 an additional coastline reconciliation with Landplan. Changes to the Boundary-Line tide lines, plus natural and gradual changes to rivers and streams have been implemented along-side the previous boundary/coast association to enhance the MHW FC0071.

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 Landplan. A consequence of this is if Boundary-Line is superimposed upon boundaries in basic scales Land-Line 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.

Boundary-Line output resolution

A suggested output within 25% of the source scale (1:10 000) should allow all data to be plotted or displayed without distortions occurring:

Country England Scotland Wales
 
No. of files 656 100 68
Size 196 Mb 234 Mb 39.9 Mb
Format NTF NTF NTF
 
No. of files 2772 537 351
Size 412 Mb 289 Mb 62.5 Mb
Format Shapefile (nested) Shapefile (nested) Shapefile (nested)
 
No. of files 30 24 24
Size 409 Mb 285 Mb 62 Mb
Format Shapefile (layered) Shapefile (layered) Shapefile (layered)
 
No. of files 1848 358 234
Size 469 Mb 316 Mb 71.5 Mb
Format MID/MIF (nested) MID/MIF (nested) MID/MIF (nested)
 
No. of files 20 16 16
Size 466 Mb 314 Mb 71.2 Mb
Format MID/MIF (layered) MID/MIF (layered) MID/MIF (layered)

More Information

More detailed technical specifications for the NTF, Shapefile and MID/MIF data formats can be found in the Technical Specification section of the User Guide. This can be downloaded from the following page: Download User Guides

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