Map Group Properties Dialog Box, General
Use the Group Properties dialog box to change the group expression for a layer. The group expression specifies how analytical data that has a relationship to spatial data is aggregated for each map element on the layer. By default, the group expression is the set of match fields that was specified for the relationship between the spatial data and the analytical data.
For example, for a bubble map that displays city locations and population size for a country or region, the match fields include city name [City] and region name [Region] because there can be multiple cities with the same name. The corresponding group expression includes two fields: [City] and [Region].