Catchment area

A catchment area is the collection of zones that can be reached within a specific ​travel time for a given mode of transportation. The catchment area can be subdivided into a primary, secondary and tertiary catchment area. 

The travel times are typically calculated in such a way that, when applied to the entire network, the primary catchment area represents 25% of current sales, the secondary catchment area represents 50% of current sales, and the tertiary catchment area represents 75% of current sales.

In other words, the primary catchment area corresponds to the isochrone of which the zones represent 25% of the current sales for the entire network. While the travel times are derived by looking at the entire network of locations, it can be applied to a single location. 

Performing an analysis within an isochrone is a location centric approach.