Abstract：This article sought to explore urban spatial partition from a point of view of street density, in order to identify the geometric
mechanism of generating urban areas. Taking the historic centres of both London and Beijing, London Docklands and notional
examples as studying cases, it identified that the change rate of street density is a main geometric factor in the partitioning of
a city, and such change rate is embodied by the degree of connections among all the streets picked out by different radii. This
also has the kind of relationship with the classification of urban functions.
