The data-intensive and computation-intensive characteristics of the geo-processing require scalable, flexible, and distributed geo-computing platforms. We employ P2P and Grid technologies to construct a prototype of P2P-Grid GIS, which can integrate distributed spatial data and computing resources to accomplish complex and large-scale spatial processing tasks. The JXTA is a general P2P toolkit originally used in our system. It has many modules and functionalities unnecessary for the prototype, which prove to decrease the system performance. Therefore, we design our own P2P communication scheme called CoreP2P. In this paper, we firstly give a brief description of the architecture of P2P-Grid GIS. We also identify the group communication requirements in the P2P-Grid GIS, which include spatial data transfer and control message transmission. Then, we discuss the components of CoreP2P and their respective
functionalities in detail. Finally, we build the P2P-Grid GIS based on CoreP2P and compare the performance with JXTA-based system.