You use a device called a ADVANCE MAP!!!!!!!!!!!!!
The answer above is probably not what you were looking for (unless you mean map layout then yeah, that's it). I'm sure there's some texture editing software out there. I'd highly recommend looking at wahackpokemon.com for good GBA utilities, some being Emerald-exclusives if I'm not mistaken.
download Advance Map
there is no such thing as an ActionReplay for a map editor, you have to be pro to use one like a ROM and a map editor, but no-one has been able to edit the maps in Pokemon diamond yet because of their 3D values
You can´t change starters in advance map but try downloading advance starter.
Use action replay DS for Pokemon Diamond
To get the mystic island on Pokemon Emerald you must acquire the Aurora ticket, Old sea map, or Mystic Ticket from a live Nintendo event. These allow you to travel to Naval rock, Birth and Faraway island to encounter legendary Pokemon.
you Cuold use the cheat-cheat book! Be careful Don't use emerald the areas are different . But you can use sapphire.
By getting an Editor for Pokemon Emerald that allows you to modify the sprites...
there is no such thing as an ActionReplay for a map editor, you have to be pro to use one like a ROM and a map editor, but no-one has been able to edit the maps in Pokemon diamond yet because of their 3D values
In the top left of the map.
No, there isn't. The legendary Pokemon for emerald is raquaza and that's it. when you finish the Pokemon league, you finish the game.
Use your map domb ass
You can find people through the map who want to trade Pokemon with you.
Use the map on your PokeNav (it helps)
Only by a Nintendo event.
If You have a Pokemon that knows FLY, fly to Littleroot town toward the bottom of the map.
you can get it at the fiery path near lavaridge town.
Buy the map of Asia
TO map hack on Pokemon emerald get a celebi and talk to may. then go to altering cave and look at your map for 3 minutes.