Where is the town map in Pokemon sapphire?

there is no town map, you get a pokenav though from the big company in the game around the second or third gym battle that'll work better than a town map. just play the game, you'll get it.

there is olso one in every Pokemon center

*edit* The Pokenav is given to you by Devon after you retrieve the Goods package from the Aqua grunt in the cave outside of Rustboro right after you battle Roxanne for the first badge. - AliisaK