A Web GIS system has a major issue of serving the map data to the client applications. Since most of the GIS services provide their geospatial data as basic image formats like PNG and JPEG, constructing those images and transferring them over the internet are costly operations. To enhance this inefficient process, various approaches are offered. Caching the responses of the requests on the client side is the most commonly implemented solution. However, this method is not adequate by itself. Besides caching the responses, predicting the next possible requests of the client and updating the cache with the responses for those requests provide a remarkable performance improvement. This procedure is called &ldquo / prefetching&rdquo / . Via prefetching, caching mechanisms can be used more effectively and efficiently. This study proposes a prefetching algorithm called Retrospective Adaptive Prefetch (RAP). The algorithm is constructed over a heuristic method that takes the former actions of the user into consideration. This method reduces the user-perceived response time and improves users&rsquo / navigation efficiency. The caching mechanism developed takes the memory capacity of the client machine into consideration to adjust the cache capacity by default. Otherwise, cache size can be configured manually. RAP is compared with 4 other methods. According to the experiments, this study shows that RAP provides better performance enhancements than the other compared methods.