1. A method of simulating a virtual world, the method comprising: processing, by a simulation engine running on a simulating computer and having access to a database storing a plurality of terrain configurations each identified by one of a plurality of characters, one or more map nodes in a map of the virtual world, each map node having a map set comprising an array of various ones of the characters, the processing including using the array to identify one or more of the plurality of terrain configurations and inserting the identified one or more terrain configurations into the virtual world; wherein processing the map nodes comprises, for each map node, stacking vertically, in the order in which the characters appear in the array of the map set, the terrain configuration associated with each character.