Many Government bodies and agencies in the UK still publish postcode data using Easting and Northing co-ordinates. Although this may be useful for some, many software systems, such as Tableau, don’t natively support this and prefer the more universally used Latitude and Longitude coordinate system.
Converting to and from these coordinate systems is not a perfect science. The process is an approximation as it attempts to convert 2-dimensional mappings onto a 3-dimensional object, along with taking account of some of the obscurities of the OSGB36 grid system. You can read more about the UK’s grid system at the Ordinance Survey. Read more