Geocoding

A common task within GIS is geocoding; the process of plotting postcodes within a GIS using an address locator. Cleaning the data for this process requires several steps. The format requires postcodes to be a length of 7 characters. This is easily achieved using the following formula in Excel:

=IF(LEN(A2) = 6,REPLACE(A2,3,1,MID(A2,3,1)&” “),IF(LEN(A2)=7,A2,IF(LEN(A2)=8,SUBSTITUTE(A2,” “,””))))

This works for postcodes of lengths 6,7 and 8. Other lengths can be added but it is rare you would encounter these. Save this as a csv file, ensuring the column has a header.

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Processing OS Codepoint Data

Working in a professional GIS environment,you will undoubtedly be dealing with Ordnance Survey data – whether open or private. One of the most useful of these is OS codepoint which provides a precise geographical location for 1.6 million postcodes within Great Britain.

This is the basis for geocoding, one of the most commonly completed tasks in GIS. This posts describes the method for creating an address locator ready for geocoding.

1. Firstly, load the data from the CD and delete (or use to a create a new address locator) the bt.csv file which represents Northern Ireland.

2. Then merge the csv’s together using the command line (make sure you are in the directory where the files are stored).

copy *.csv insert_new_file.csv

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