This paper explores the evolution and spatial organization of urban communities in a daily cycle of a city using scalable methods of social network analysis. Using mobile phone network records, we have observed spatial patterns in community structures at ne spatial scales which are most likely related to the activities typical to the dierent functional regions of a city. It is known that interactions between dierent parts of the city are subject to a distance decay, moreover, our ndings show that regardless of the time of the day or current activity, people tend to communicate within a spatially enclosed community. Furthermore, we have investigated transitions and transformations of these communities at the temporal scales of several hours related to the cycles of human movement and activities in a city.