The uplink inter-cell interference is a major impairment in wireless systems. In this paper, we provide a geometrical-based framework for its analysis in networks with convex polygonal coverage area. Algebraic expressions for the Angle-of-Arrival (AoA) statistics of the uplink interfering signals are obtained. Simulation results validate the model. Representative examples show the dependence of the AoA on system geometry and demonstrate the relation between uplink interference and the radiation pattern of the receiver antenna. The proposed model is a generalization of previous studies in simpler geometries. It is a useful tool for the design, simulation and performance evaluation of wireless communication systems. The obtained expressions simplify the analysis of wireless networks and reduce the complexity and computational cost of their modeling and simulation.