What are lookup tables?

Lookup tables (LUTs) are used to convert census data from an official source geography to a user target geography. The official source geography (e.g. areas A to D in the figure below) is the geography for which the census area statistics are supplied. The target geography zones (areas 1 to 4 in the figure below) are the areas for which a user might need the census data.

The simplest lookup table would simply be an index that represents the intersection between the source and target geographies, as shown in the first two columns of the figure.

The third column of the lookup table holds the weights used in the conversion. The weights, which might be the proportion of households in the intersecting area, are necessary because household counts are not evenly spread across a zone. Such a lookup table enables researchers to convert data from census areas to postal areas at a small scale.

More information about lookup tables is provided in CHCC CAS Unit 11: Using Data from Different Sources: Consistent Geographical Units [Note: This link opens in a new window]