In the urban areas of Europe and USA, a significant part of the final energy consumption corresponds to the buildings heat demand. Given the challenges related to climate change, to energy security and dependency from fossil fuels, modifications of the energy infrastructure and increasing the share of renewable energy represent a priority in urban energy planning. This study proposes a modeling approach for the total cost optimization of heat supply within a given area considering the integration of geothermal energy resources. It aims at structuring and identifying promising district heating sites in which technical and economic criteria are maximized. The spatial structure of these sites is defined according to the availability of the heat resource. The presented approach handles Geographic Information Systems (GIS) data for geothermal resource, heating demand and buildings location. This spatial consideration constitutes the basis of the optimization of the geothermal integration. The methodology of this work is applied to the case study of a deep aquifer in the city of Lausanne, Switzerland (140'421 inhabitants). The territory is segmented into 18 coherent subsystems according to the geographic location and the heating demand of the buildings. A multi-period model, taking into account the seasonal variations of the heating demand, integrates all the subsystems. Optimization is used to identify the subsystems, in which a centralization of the energy conversion technologies (including geothermal energy) and a construction of a new District Heating Network (DHN), is economically suitable. Scenarios based on parameters such as resource prices and technology costs are evaluated through economic indicators. The analysis of the results demonstrates that spatial heating demand's density and fossil fuels' costs are strongly involved in the profitability of the heating centralization. They contribute to the most part of the total annual costs. According to the scenarios and the zones in the city, the dependency on the fossil fuels can be reduced up to 40% by integrating geothermal energy. Besides the obvious advantages related to CO2 emissions and Global Warming Potential (GWP), geothermal energy integration appears in some case as a competitive alternative in terms of cost.