Heading east from Cerulean, the route quickly utilizes the rocky terrain of the area, hopping down a ledge and passing a Trainer, making this portion of the route a one way, eastbound only passage. Turning east, the route passes an opening to the south that leads to another Trainer and TM30 (Teleport) in Generation I, or TM40 (Aerial Ace) in Generation III. Moving away from the passage, Route 9 comes to a four-way intersection. To the north is the one way, westbound only passage that returns to Cerulean and is occupied by two Trainers and a grassy area containing wild Pokémon. To the south is a long passage that ultimately results in a dead end, containing one Trainer and a Burn Heal in Generation III. The main path of Route 9 takes the east fork.
To the east of two hills connected by ledges, the route turns north into the path of another Trainer. The route also comes to a three-way intersection here, with a fork to the west leading to yet another Trainer and a small patch of grass. Route 9 continues northward, turning east, passing another Trainer and turning south to the northeast of another small hill. After hopping another ledge that makes the passage east of the four-way intersection a one way, eastbound only path (and which utilizes the dead end passage, which is bordered to its north by a ledge for most of its length, as the westbound only path), the path crosses ways with another Trainer as it turns east.
Just east of the Trainer is a pair of ledges that allow Trainers heading west from the Rock Tunnel to reach the four-way intersection that ultimately leads to Cerulean. Farther east, the route comes to an end at the western extent of a large grassy area, at which the path becomes Route 10.
Only a few cosmetic changes are present between Generations I and III. The normal tree on the side of the cut-able in the west of the route is changed to a fence and the same kind of tree south of the nearly tall grass is changed to a rock. Some hills are bigger, and all of them are made taller in FireRed and LeafGreen, adding another hill above. Also, the flowers in the west entrance are replaced by trees.
In Generation II, the route was shortened by roughly 30%, and the corner between it and Route 10 belonged to it instead of belonging to Route 10 as it does in Generation I and III, making the north entrance to the Rock Tunnel placed practically in this route by three steps. Interestingly, the only way to enter the cave is entering Route 10 as the half of the Pokémon Center blocks the way. Also, almost all items were removed from the route and the number of Trainers was reduced to six. However, five of the six remained in positions occupied by Trainers in the other Generations.
The fence and the tree barricade
Many changes are made in this route. The cuttable tree is removed, the tall grass in the west side is slightly moved to the south, the shape of the same grass is also different, the ledge north of the signpost is removed, as a new ledge is added near the center grass, and a hill is added to the route to give it a more in-depth feel. South of the east tall grass, a new fence with four cuttable trees is added replacing the ledge north of the Poké Center, one of these trees not being necessary to pass through the grass. Like in Gold, Silver and Crystal, the corner between it and Route 10 belonged to this route; however, this time the Rock Tunnel entrance is not placed in the route.
For decorative purposes, rocks are added in some hills, as are the flowers near the Pokémon Center and two more hills in the east river. This river is not a dead end to the north like in previous generations; this time the water goes north, but it's still impossible to advance due to rocks blocking the way. The west-to-east part of the river is significantly shortened. Also, the trees in the west entrance are replaced by an extension of the south hill. The fence with the trees mentioned above is very similar to the tree barricade between the Pokémon Center and the Rock Tunnel in Route 10 in Generations I and III.
In the manga
Route 9 in Pokémon Adventures
In the Pokémon Adventures manga
Route 9 was featured from Can't Catch Caterpie! to The Primeape Directive, where Blue and Yellow trained at the mountainous areas of the route in preparation for the upcoming battle against the Elite Four. Soon after arriving at the mountains, Yellow encountered a Caterpie, which had followed her all the way from Celadon City. Following Blue's instructions, she eventually caught it and added it to her team, nicknaming it Kitty. As a result for her battles against Caterpie while trying to catch it, Yellow's Rattata, Ratty, evolved into a Raticate, much to Yellow's shock, since she hadn't been aware that Pokémon could evolve.
After training together for a while, Blue and Yellow went on their separate ways by sea. Since Yellow didn't have a Pokémon that could Surf yet, she instead boarded the bypassing S.S. Anne to Vermilion City.
In Pokémon Adventures, the industrial waste from the unfinished Power Plant to the south has spread all the way to this route, causing erosion and killing off most of the local plant life. This has also affected the food resources of the Pokémon living in the area, including a pack of Mankey, forcing them to travel far and wide in search for anything to eat.