Route 20 (West Entrance)
This route is somewhat split into two parts: East and West. The only thing preventing you from going eastward is a Hiker who claims that you need a badge to pass. In terms of your rival's location to give him the map, well he is not here, but there is an opening to a ranch to the North, and your rival has not picked up any badges either, so that must be where he is.
Before going through, there is a Paralyze heal laying around (probably for some of the Pokémon contained in the ranch.) Also, if it is Autumn time when playing this game, you can get a Poké Ball by going across a bed of leaves.
There are some new Pokémon in this area, so those may be worth going over. Firstly is Sewaddle, who is a Bug and Grass type, which is not that great of a type defensively. Offensively, this Pokémon's final evolution is fast and offensive, with really good move coverage to boot.
Next is Pidove, which is really common to find in all seasons except Summer. Pidove's evolutions are fast, but they cannot dish out much damage, because its physical movepool does not compliment its 103 Attack stat. By the late game, you are left with something that desperately needs replacement, because Aerial Ace and Air Cutter are just not cutting it.
Lastly is Sunkern, the first non Generation V Pokémon that can be found, and it does not put up a good front. Sunkern has the lowest base stat total (total of all stats) of any Pokémon ever. Its evolution, Sunflora, is a good Sp. (Special) Attacker, but nothing else. Grass is a pretty bad defensive type as it is, but Sunflora has a base 30 Speed stat, so it is very rarely going first. A must pass.