MapProxy is an open source technology used to create and serve up map caches. It is a middle-man between existing web map servers (like MapServer or GeoServer) and web map clients such as OpenLayers and GoogleEarth. The following diagram helps illustrate the concept.
How Does it Work
Clients connect to MapProxy like they would any other Web Map Server. MapProxy parses the map request and retrieves the corresponding map data from a map cache. If the map cache does not contain the corresponding map data, MapProxy issues a request to the Map Server. MapProxy caches the response in the map cache for subsequent requests.
What Makes MapProxy Unique
Map caches are nothing new. Google Maps really popularized the notion back in 2005. ESRI ArcGIS, KaMap and GeoWebCache all rely on a map caches for fast map rendering. What makes MapProxy somewhat unique is its ability to respond to arbitrary WMS requests.