A geographical information system (GIS) is a system that captures, analyzes, and manages any spatially referenced data. One common problem in the GIS community is how to generate and publish customized Web maps. The existing solutions either deal with spatial data directly which does not allow for applying the customized features, or require and rely on advanced and specialized programming skills. We believe that applying service oriented architecture (SOA) to GIS can improve the interoperability of different GISs and can combine different GISs to provide customized Web maps using a Web service orchestration language. In this paper, we present a novel solution that applies SOA and business process execution language (BPEL) to orchestrate Web map services into a customized Web map. The process of requesting a map layer from a map service provider is an invocation of the remote GIS map service. The process of generating a customized Web map becomes a process of combining different GIS map services into a BEPL process. This makes it possible to generate the business logic in BPEL first and then execute it to obtain a new map. Ideally, once the process is generated in BPEL, it can be plugged into any GIS system. This new solution generates a single new map after all layers are combined together, while the existing asynchronous JavaScript and XML (AJAX) based solution gives a stack of map layers and the layers cannot be saved as one map. We have implemented a framework for the map creator to combine map layers published by different map service providers into a single new map, save the map composition process logic, and publish the new map as a service. Also, the framework provides map brokers more control of and easier interaction with the map composition process.