While traveling the Amsterdam metro the other day a person standing behind me told another person that you could identity a city’s center by looking at its subway network. The center is oftentimes inside an oval with lines leaving the oval.
Even though this statement is not true for the general case, it contains the valid thought or suggestion that structure is at least correlated with and maybe indicative of meaning. There is a sense in which structure, a river for commerce, roads for transportation, has made it possible for a city to be formed at a certain spot (structure predating the city). Then, once the city grows, structure is added and/or changed, e.g. by adding subways.
In some sense knowledge of the structure of transportation and communication channels induces knowledge of where cities are. If we would have to explain to an outer-worldly visitor what a ‘city’ is, both showing a transportation map and giving a historic account of the original transportation route (e.g., the main river around which a city was formed) seem apropriate ways to start.