Mapping virtual process topology to physical processor topology is one of the most important issues in parallel computing. The mapping problem for switch-based cluster systems of irregular topology is very complicated due to the connection irregularity and routing complexity. This paper proposes two mapping schemes for irregular cluster systems, which try to map the nearest neighbors in the process topology to physically adjacent processors. In addition, an application-oriented performance metric, weighted cardinality, is introduced to represent the quality of mapping. A simulation study shows that, for a virtual topology of a 16/spl times/16 mesh, the proposed mapping schemes result in better mapping quality and about 15/spl sim/20% shorter communication latency compared to random mapping. The proposed algorithms should also be beneficial when they are applied to metacomputing and cluster of cluster systems, where the communication costs are an order of magnitude different depending on the relative position of the processor nodes.