Before revision:  A set of communities can be defined as any partition of a population such that travel/social contact within each community far exceeds that between them (e. g. the U.S. could be partitioned by state or commuting zone boundaries).
After revision:  A set of regions can be defined as any partition of a population such that travel/social contact within each community far exceeds that between them (e. g. the U.S. could be partitioned by state or commuting zone boundaries).