The world map in my game will be stored on the server, because the players will be able to expand and modify the map. So the client must download the map as it moves along. As I see it there are two alternatives: 1. The server PUSHES out the map and keeps track of the sectors sent to the client. Lets say the client moves 10 steps east, the map is updated, then he turns back and moves 10 steps west, the client already has that part of the map. The bad side of this is that the server will have to keep a cache for each client. 2. The client PULLS the map, based on his map cache. This can get ugly, because we don''t want to trust the client. But the client ultimately knows what he has cached... Suggestions?

2. isn''t such a big issue as far as trusting the client goes. If someone hacks the client, the worst that they can do in this aspect is not download any parts of the new map, in which case they will just find playing the game plain hard, or continuously download the map which may strain their connection, and strain yours a little more.
An idea might be to keep a "last modified" value for each sector of terrain on the server, and the client keeps a cache of these values with the sectors it has downloaded. When it moves in range of a sector, it checks the sectors timestamp and downloads if neccessary.