Why are there differences in boundaries?
Two boundary data sets?
Boundaries are shown in two OS products:
Boundary-Line
OS MasterMap Topography Layer
Boundaries have been shown on Ordnance Survey Mapping for over 100 years. These were then digitised as lines into Land-Line from the 1970s and subsequently into OS MasterMap Topography Layer since 2001. They were captured and maintained at large-scale (1:1250/1:2500 scale).
Since the mid 1990s Boundary-Line has existed as an authoritative polygonised dataset of political and administrative boundaries initially captured and maintained at 1:10000 scale although more recently being maintained to large-scale data.
Boundary-Line shows only boundaries that are Operative and is the authoritative dataset for boundaries in Great Britain. OS MasterMap Topography Layer may show boundaries before they are Operative, or there may be a slight delay before being updated after they are Operative.
Who is responsible for the boundaries?
In Great Britain there are three national Boundary Commissions, one each with responsibility for England (BCE), Wales (BCW) & Scotland (BCS). These are responsible for UK Parliamentary constituency boundaries.
Local government electoral arrangements are reviewed by the Local Government Boundary Commission for England, the Local Democracy and Boundary Commission for Wales and Boundaries Scotland. These include making changes to wards and electoral districts. LDBCW and Boundaries Scotland also look after the Scottish and Welsh devolved parliaments. Local Authorities are responsible for Parish and Community boundaries.
The outputs of these organisations (changes to boundaries published in Statutory Instruments, Boundary Orders and maps) all then come to Ordnance Survey to be included into Boundary-Line and OSMasterMap Topography Layer
Data Comparison
The authoritative boundaries dataset for Great Britain
Initially captured at 10:000 scale, currently maintained against larger-scale OS MasterMap data
Contains Administrative and Political Boundaries
All data is polygonised and themed by boundary type (County, Districts, Unitary Authorities, Parishes, Westminster Constituencies, and so on.)
All polygons include attribution such as name, type and links to ONS codes for the different boundaries
Published twice a year in May and October
Available as Open Data for anyone to use
More detail can be found on the Boundary-Line pages of the OS website
Why are the 2 products different sometimes?
The main reason for differences between boundaries in Boundary-Line and OS MasterMap Topography Layer is to do with the scale they were captured at:
“Boundary-Line for England and Wales was initially digitised from Ordnance Survey’s boundary record sheets at 1:10 000 scale (or, in some cases, at 1:10 560 scale).” OS Website
“OS MasterMap Topography Layer provides the most detailed and accurate large-scale representation of Great Britain available from Ordnance Survey.“ – OS MasterMap Topography Layer Technical specification document
As these show, Boundary-Line was initially captured at a smaller scale than OS MasterMap Topography Layer. Boundary-Line is still the authoritative dataset and although these slight differences exist in places, they are normally no more than a few meters and addresses (and therefore citizens) should not fall inside the wrong Ward, County, Parish, etc.
Which boundary data should I use?
This content has been developed from what was originally a Lightning Talk PowerPoint slide set. These slides are available to PSGA members to view and download from the PSGA members area of the OS website
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