In order to calculate data for custom areas based on postcodes, Local Insight identifies all the OA areas covered by the uploaded postcodes and then calculates the data based on those component OAs.

Local Insight then apportions data for that collection of OAs and their value is the value for your custom areas.

### Apportioning

The process of modelling data published at higher geographies (LSOA / MSOA) to get values for smaller geographies.

**'Sum' type apportioning:**

- For data that represent counts (for example numbers of people or amounts of money) we use 'sum' type apportioning (sum type since to aggregate this data to larger geographies we simply sum the values of the component areas). When apportioning, the value of the larger area is divided up amongst smaller areas according to the area's population. The naming is a little confusing here - the parent area is the area that data is apportioned to (in this case the geographically smaller area) and the component area is the area that data comes from.

**'Weighted-sum' type apportioning:**

- For data that represent averages (for example standardised mortality ratios) Local Insight uses a different approach. When aggregating rate data the value of a large geography is given by the weighted sum of the component area values, with area populations used for the weighting. When apportioning such data, we simply assign each of the smaller component areas the same value as the parent area. This ensures that the weighted sum of the smaller areas matches the value of the larger area, avoiding discrepancies that would arise when apportioning to areas with small populations.