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UK Postcode Geo-referencing

We have point data available at 4 levels of postcode (Full, Penultimate Character, Sector and District level) in either a) National Grid metres or b) Latitude & Longitude whether in Degrees Minutes Seconds format or as numeric Decimal Degree values. We provide the following detail to assist overall understanding of content, file statistics and coding ratios to enable an informed selection of that best suited to your application. If we can assist through advice based on our experience we will willingly do so.

  • refer to postcode system for explanation of code structure and its constituent elements
  • circa 93% of the 1.7million records are geo-referenced; this arises due to the fact that
  • geo-referencing is available for 121 of 124 Postal Areas, not for Guernsey, Jersey or Isle of Man (GY, JE & IM) or for the unique codes assigned to POBoxes
  • allowing for the above factors, geo-referencing is available for over 99% of other codes
  • the balance for which it is not, tend to be specialised non-geographic codes for the likes of Government Departments, Financial Institutions, large Mail Order Businesses, etc
  • non geo-coded records impact all 4 files and overall % coding of such differently for technical reasons concerning UK code structure; this is correct and the % should not be misread as relating to "quality"
  • standard code geo-referencing has been to what is termed "100m resolution", codes are assigned the geo-reference of the lower left corner of 100m square in which they are located
  • it is a misconception to think codes have unique geo-references at such resolution; the 1.7million codes are covered by approx 1.1million values
  • for most this resolution provides a sound solution basis. Many applications especially "nearest to/locator" functionality do not require use of 1.7m full codes ~ this we explain/illustrate later
  • to position a code/property correctly in a street, in say high resolution mapping, you need to use greater than 100m resolution i.e. 10m/1m - contact us if this is relevant to your application
  • we detail below the 4 file levels; example use the postcode "BN1 1EE" of the Brighton Royal Pavilion

Full Postcode - 1.7+ million records
For those needing to use the full postcode, possibly because of linkage to the likes of "automated address infill/verification" ~ to achieve such at Street level refer to Street Address Database. Overall statistics and coding ratio at this level are provided in the points above.

Version Mb Fields Example as ASCII Delimited Comma Separated Text
National Grid 64 4 "BN1 1EE","053120","010410","TQ30"
Lat/Lng DMS 74 2 "BN1 1EE","50N49'19.222" 000W08'17.329"
Lat/Lng Decimal 53 3 "BN1 1EE",50.822006,-0.138147"

Penultimate character - 140,000 records
We conceived and constructed this file to provide a high resolution solution (illustration) with a "small" file. It offers a quality alternative to the 1.7m record file (above) with negligible "real world" difference to many applications and 12x greater detail than the lower Sector level file (below) itself ideal to many applications. When truncating UK codes by 1 character, the UKs unique POB & specialised codes distort what one might expect to be the files coding ratio (87%); this is correct and should not be a concern. The approx 125,000 geo-coded records of the file are covered by 123,000 values; at less than 8% of the size of the full file, it has a significantly higher unique value code ratio (98%:67%). The extent of variance in a value assigned to a record in this file against that to a full code may potentially vary most widely in extreme rural areas, but for the majority of applications is immaterial.

Version Mb Fields Example as ASCII Delimited Comma Separated Text
National Grid 5.0 4 "BN1 1E","053124","010413","TQ30"
Lat/Lng DMS 5.6 2 "BN1 1E","50N49'18.743" 000W08'17.185"
Lat/Lng Decimal 4.0 3 "BN1 1E",50.821873,-0.138107"

Sector Level - 11,000 records
Sector level (illustration) has long been used in analysis, commercial, administrative, logistic, planning, marketing, insurance and statistical purposes. This file provides geo-coding for to the first part of the Inward element of the postcode Our file includes the PostTown. Geo-references are provided for 91% of records (see earlier comments re GY/JE/IM, POBox & specialised codes). Though rare, more than 1 PostTown can apply to a Sector e.g. Bromley and Keston to "BR2 8"; where this occurs our file holds a record for each Sector and Town combination. The Sector level file should not be thought of as a low level solution (for perspective it is 100x more detailed than the use of County) and is widely/popularly used ~ that said, our Penultimate Character file above is 12x more detailed Sector.

Version Mb Fields Example as ASCII Delimited Comma Separated Text
National Grid < 1 5 "BN1 1","053110","010422","TQ30","BRIGHTON"
Lat/Lng DMS < 1 3 "BN1 1","50N49'21.684" 000W08'24.050"","BRIGHTON"
Lat/Lng Decimal < 1 4 "BN1 1",50.822690,-0.140014,"BRIGHTON"

District Level - 3,000 records
This file provides geo-referencing for the Outward element of the postcode (illustration) and is perfectly suited to many applications where higher resolution is not required or is indeed deliberately to be avoided say for the sake of inherent confidentiality to the intended application. Geo-references are provided for 97.5% of records (see earlier comments re GY/JE/IM, POBox & specialised codes). Though the lowest level resolution of the 4 files, it is 27x more detailed than would be achieved by using County.

Version Mb Fields Example as ASCII Delimited Comma Separated Text
National Grid < 1 3 "BN1,"053108","010640"
Lat/Lng DMS < 1 2 "BN1","50N50'32.006" 000W08'22.340"
Lat/Lng Decimal < 1 3 "BN1",50.842224,-0.139539"

 

Note re Coordinates: for the sake of consistency in Easting and Northing field presentation, we provide National Grid coordinates as a fixed 6 digit format, the latter being required for the Northern most part of Scotland. Accordingly using the example code "BN1 1EE" = "053120","010410", you would import and convert the fields to numeric values and a) divide by 100 to yield 531.20 & 104.10 Kms East & North respectively or b) multiply by 10 to yield 531200 & 104100 metres East & North respectively. Additionally if working with coordinates, have regard to the fact that N.Ireland (single Postal Area "BT") values are based on the Irish National Grid, accordingly if utilising such you may wish to isolate them to a separate file.

 

Evox Facilities Ltd, 9 Hillbrow, Reigate Road, Reigate, Surrey, RH2 0QX England
Tel/Fax: +044 (0)1737 247333