In the ticketing system of the British rail network, tickets are normally issued to and from individual stations. In some instances, when there is more than one station in a town or other locality—especially where these are on different routes—it may be desirable for passengers to be able to travel to one station and back from another, or more generally to be able to choose which of the stations they wish to travel to. To accommodate this requirement, British Rail introduced a series of station groups: notional "common locations" to which tickets from stations outside that group would be issued.