Multiple wireless devices jointly create and maintain ad hoc networks; their employment is favored to happen in a variety of environments with distinct topological characteristics. Diversified environmental conditions are expected to vary network performance. In fact, obstacles, buildings and/or mountains may act as either barriers, or source of noise for the radio signals. Nevertheless, most of the previous performance evaluation studies based on simulation, neglected this consideration; they used simulation models that were too simplistic, and too narrow (i.e. idealistic) in their scopes. With this paper we propose a new, complete and realistic Urban Mobility Model (UMM). It models realistically users motion, and radio signals propagation in a citylike scenario. Our aim is to study the effects of realistic network simulation on routing performance. The results prove that a realistic scenario with roads and buildings has a significant impact on routing.