Random Battling on World Maps

I have noticed that I can't change the monsters that randomly occur on a map according to where they are. For example: I would be fighting rabbits in a meadow. Then if I where to fight in a desert, the rabbit still appears. How can I change this?

which rpg maker r u using?  in 2003 u can just right click on the map on the side and create areas that could have different monster battles.  not sure about xp.

If it's XP, just make little choke points between the areas, and cover them with events. When the player hits the event, make it change which groups appear.

You further explain the choke points (rpg maker xp). I am a quite the noob.

Well it's not really an RMXP term, just slang (I think it's slang). What you do is instead of having a wide open entrance, sort of like a field, you use nature to gate it off, so you can only enter from a certain spot. Like so:
       __________________________
      /    |                                       \
                                                    \
ENTRY WAY --->                             |
      ___                                         /
      \    |                                       /
 

Parallel process common event that checks if you are on a terrain tag 1 tile ($game_player.terrain_tag == 1). Set bushes/grass to be on 1 in the Tileset data. Now just use a random number and check if the player is moving ($game_player.moving?) and if yes, wait 4 frames, check the random number. If the number fits, engage in battle. You can use SCRIPT in the conditional branching (4th tab), that's where you put the stuff in I bolded.