Urban power supply system (UPSS) is a part of the region or the state power supply system. UPSS development is closely connected with region power supply system development as a whole. The decision of questions of long-term and middle-term planning of UPSS development occurs in the conditions of incompleteness and uncertainty of the initial information. Nevertheless and in these conditions the acceptance of development strategy should be based on perspective electric loads of urban transformer substations (TS). There are difficulties with a rational placement of substations in the city with the developed infrastructure. Such problem by theoretically grounded approach to rational formation of UPSS is solved. The hierarchical structure of the organizational construction, voltage levels and load densities is considered. The mathematical and geometrical modeling of service areas for transformer substations of different voltage is fulfilled. The method of graphic placement of transformer substations in the city territory for new substations at existing structure of networks is offered. The aim of the work is to present the new uniform approach which allows finding a rational decision for new substations' placement in cities with developed infrastructure on the beginning design stages in conditions of the information uncertainty. The calculation program Microsoft EXCEL and the graphic program AutoCAD are used for realization of method.