Hoenn is a primarily tropical region with a wide variety of environments ranging from deserts, to rainforests, to active volcanoes. It is heavily forested overall, and most of its major cities are placed along the coast. Several islands lay off the shores of the mainland that are accessible by ship or water type.
Plenty of exotic Pok?mon are native to these lands and ripe for capture if a trainer is willing to search for them through harsh terrain.