Census data are aggregated within different boundaries by assembling small geographical 'building bricks' to which the data are coded. The most adaptable and unchanging 'building brick' is a National Grid co-ordinate reference. A grid reference to a resolution of one metre gives an address, and people at it, a unique geographical location. Data with such references can be captured and aggregated for any area with a boundary represented by a line of co-ordinates - termed a digital boundary.

Every record on the output database of the 2001 Census has a co-ordinate reference to a one metre resolution, as well as a postcode and more conventional area codes. This allows the data to be aggregated to any area - current, new or old, or ad hoc, changing or stable. It was also the basis for the production of improved small areas for the presentation of statistics - the Output Areas.