In rustboro city there is a large building called the Devon corporation the president of the corp makes gadgets called pokenav's this handy machine has many features to it, it provides a map, condition info on your Pokemon (basically it shows the stats for contests), Ribbon info and also it shows profiles of trainers called trainer's eyes you can use this feature to also see trainers who want to rebattle you they will have a pokeball icon next to there name. When you give the Devon goods back to its original owner you will be taken to the president of Devon corp to receive a free pokenav!
Chat with our AI personalities
Apart form the Battle Island no there is no second map or extra islands.
Actually scrap that,you need the old sea map to get there but you have to trade it with someone who has the old sea map on Pokemon ruby/sapphire
Pokemon Ruby has Pokemon that Pokemon Sapphire does not and Pokemon Sapphire has Pokemon that Pokemon Ruby does not.
There is no town map. You might be referring to the Pokenav, which is Ruby, Sapphire and Emerald's version of the Town Map. You can get it at Rustboro City from the Devon Corporation's President.
Evee is not availiable in Pokemon Sapphire.