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UK Postcode Geo-referencing

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

refer to postcode system for explanation of structure of the postcode string and its constituent elements
93% of the 1.76 million records are geo-referenced; this percentage arises due to the fact that
geo-referencing is available for 121 of the 124 Postcode Areas, not for Guernsey, Jersey or Isle of Man (“GY”, “JE” & “IM”) or unique PO Box codes
allowing for both of the above factors, geo-references are available for 99.9% of postcodes
the few records for which it is not, tend to be specialised non geographic codes for Government Depts, large Mail Order Businesses, etc
standard geo-referencing is to “100m resolution”, codes being assigned the geo-reference of the lower left corner of 100m square in which they are located
misconception to assume postcodes have unique geo-references at this resolution; the 1.76 million codes are covered by 1.1million values
for most this resolution provides the basis of a solution and many applications e.g. “nearest to” / “locator functionality” do not require use of the full postcode
to position a code/property on the correct side of a street in say a high resolution mapping application, you need 10m/1m data - contact your s/ware provider
example record below (PO1 1AF) for which we provide values at the four file levels, is the postcode of the Address Management Unit at Portsmouth.

Full Postcode - 1.7 million records

For those needing to use the full postcode, possibly because they are linking such to “automated address infill/ verification” or because having regard to the above bullet points “100m resolution” is a requirement. Overall statistics and coding ratio at this level are given above.

Version	File Mb	Fields	Example as ASCII Delimited Comma Separated Text
National Grid	64	4	"PO1 1AF","046430","010030”,"SU60"
Lat/Lng DMS	73	2	"PO1 1AF","50N47’53.253" 001W05’15.026””
Lat/Lng Decimal	52	3	"PO1 1AF",50.798126,-1.087507

Penultimate character - 144,000 records

We conceived and constructed this file to provide a high resolution solution using a small file; it offers a quality alternative to the 60+Mb full postcode file (above), yet a level of detail (illustration) far greater (12x) than the Sector Level file (below) itself ideally suited to many applications. The lack of geo-references for PO Boxes and 3 Areas explained above naturally apply to this file. However when truncating codes by 1 character, the UKs 113,000 unique PO Box records distort what one might expect to be the files coding ratio (85%); this is correct and should not be a concern. The 122,000 geo-referenced records of the file are covered by 120,800 values, it is less than 8% of the size of the full file and has a significantly higher unique value code ratio (99%:67%). The extent of the variance between a value assigned to a record in this file and that in the full code will potentially vary most widely in extreme rural areas, but for the majority of applications is immaterial.

Version	File Mb	Fields	Example as ASCII Delimited Comma Separated Text
National Grid	5	4	"PO1 1A","046450","010034”,"SU60"
Lat/Lng DMS	5.5	2	"PO1 1A","50N47’54.468" 001W05’04.784””
Lat/Lng Decimal	5.6	3	"PO1 1A",50.798463,-1.084662

Sector Level – 10,600 records

Sector level analysis (illustration) is popular in diverse commercial, administrative, logistic and planning areas. Our file includes the PostTown, an integral element to correct addressing. Geo-references are provided for 95% of records (refer to earlier comments re GY,JE & IM codes and UK PO Box postcode records). Though rare, there are cases of more than 1 PostTown applying to a Sector (e.g. Bromley and Keston both apply to “BR2 8”), where this occurs our file holds separate records for each Sector and PostTown combination. The file should not be thought of as a low level solution; viewed in perspective it is 95x more detailed than the use of County.

Version	File Mb	Fields	Example as ASCII Delimited Comma Separated Text
National Grid	< 1	5	"PO1 1","046457","010040”,"SU60",”PORTSMOUTH”
Lat/Lng DMS	< 1	3	"PO1 1","50N47’56.382" 001W05’01.170””,”PORTSMOUTH”
Lat/Lng Decimal	< 1	4	"PO1 1",50.798995,-1.083658,”PORTSMOUTH”

District Level – 2,980 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 deliberately to be avoided. Geo-references are provided for 97.5% of records (refer to comments re GY,JE & IM codes and UK PO Box postcode records). Though the lowest level resolution file, relativity is provided by the fact it is 25x more detailed than would be achieved by using County.

Version	File Mb	Fields	Example as ASCII Delimited Comma Separated Text
National Grid	< 1	3	"PO1”,"046421","010034”
Lat/Lng DMS	< 1	2	"PO1”,”50N47’54.584" 001W05’19.598””
Lat/Lng Decimal	< 1	3	"PO1”,50.798496,-1.088777

Note re Coordinates: for the sake of consistency in Easting & Northing field presentation, we provide coordinates as a fixed 6 digit format, the latter being required for the Northern most part of Scotland. Accordingly using the example code on this page "PO1 1AF” = ","046430","010030”, you would import and convert the fields to numeric values and a) divide by 100 to yield 464.30 & 100.30 Kilometres East & North respectively or b) multiply by 10 to yield 464300 & 100300 metres East & North respectively. Additionally if working with coordinates, have regard to the fact that for N.Ireland (single Postcode Area of "BT") values are based on the Irish National Grid, accordingly if utilising such you may wish to isolate them to a separate file.

Geo-reference Conversion

If you have your own geo-referenced data and require accurate conversion, Latitude & Longitude to coordinates or vice versa (WGS84, OSGB36…) email us detail of your requirement, the format / structure of your information, the number of records and conversion you require - we will gladly review such and quote if your requirement is feasible.

Email: enquiries@evoxfacilities.co.uk Tel/Fax: +044 (0)1737 247333