Increasing communication demands of processor and memory cores in Systems on Chips (SoCs) necessitate the use of Networks on Chip (NoC) to interconnect the cores. An important phase in the design of NoCs is the mapping of cores onto the most suitable topology for a given application. In this paper, we present SUNMAP a tool for automatically selecting the best topology for a given application and producing a mapping of cores onto that topology. SUNMAP explores various design objective such as minimizing average communication delay, area, power dissipation subject to bandwidth and area constraints. The tool supports different routing functions (dimension ordered, minimum-path, traffic splitting) and uses floorplanning information early in the topology selection process to provide feasible mappings. The network components of the chosen NoC are automatically generated using cycle-accurate SystemC soft macros from xpipes architecture. SUNMAP automates NoC selection and generation, bridging an important design gap in building NoCs. Several experimental case studies are presented in the paper, which show the rich design space exploration capabilities of SUNMAP.