there is no such thing as "sunset city"
In both diamond and pearl the one city is Hearthome
The sixth gym is in Canalave City of Pokemon Pearl, west of Jubilife City.
You can't go to Celadon city in Pokemon Pearl. Its from an earlier region.
Between pastoria city and hearthome city.
That is the city you start at!
Its not in a city its in a tower.
Jublife city.
i think it is in jubilife city.
You cant
south of hearthome city
There are Pokemon Centers in every town/city.
Veilstone City