Output Area (OAs) were originally created for Census data, specifically for the output of census estimates. The Output Area is the lowest geographical level at which census estimates are provided. Many other government datasets have incorporated OAs as standard release level. These can be used to compare locations based on their comparable sizes.

The minimum OA size is 40 households and 100 resident people, the recommended size is 125 households. There are 171,372 OAs in England and 10,036 for Wales, across the whole of the UK there over 230,000. OAs align to local authority district (LAD) boundaries, and also at the border between Scotland and England. The average population in an OA has increased from 297 in 2001 to 309 in 2011 to better reflect population changes. Output Areas fit within Lower Super Output Areas (LSOA).