Working paper 13 from the Economic Intelligence Unit of the Greater London Authority (GLA) assesses to what extent it is possible to construct standardised geographical definitions of cities that will allow American and European cities to be compared in a consistent manner. Building on previous work on the comparison of European cities, it extends the method to US cities. This is an interesting exercise, since US cities have a standardised methodology for determining the economic extent of their cities which is an aid to rational planning, whereas European city definitions, which have evolved in a haphazard way, do not.