Following on from an earlier post updating OS Codepoint data , this post will now look at how to process OS Codepoint with polygons. This dataset provides a polygon for each postcode, including vertical streets (represented by squares) which is where a building has more than one postcode.
1) From the data provided by OS all the shapefiles (for each postcode sector) need to be merged into one. This can be achieved using QGIS ‘Merge to one’ tool under the vector toolbar or by writing a simple python script in arcmap utilising the merge tool.
2) We are going to create two extra fields in the attribute table ‘PCOutcode’ and ‘PCSector’ – this will provide us with additional symbology options with GIS. For ‘PCOutcode’, use =RTrim(Left(Postcode,4)) to capture the first part of each postcode, and for ‘PCSector’ use =RTrim(Left(Postcode,5)) where Postcode is the postcode field and RTrim removes any trailing spaces.