You may have a record level data file, which contains a row for every sale or every customer or every postcode.
In order to plot the data in this file the system needs to convert your data to either postcode area, a district or a sector.
This conversion to a higher level is known as aggregation and will create a new summary dataset for you at the new level.
If you convert to postcode area, then all the values on the rows with a postcode within an area will be automatically added up.
The system will create a new dataset at the level you have chosen.
Record level rows will be grouped together based on the level you have selected. The values in this new dataset will be automatically calculated by adding up all record level values for the rows in each group.