From Bulbapedia, the community-driven Pokémon encyclopedia.
The Habitat List (Japanese: せいそくちリスト Habitat List) is a Pokédex feature in Black 2 and White 2. It lists each area the player has visited in Unova, along with every Pokémon the player has seen or caught that can be found in that area.
Each area's entry is divided into three parts: a field section, a surfing section, and a fishing section. The field section aggregates all Pokémon found in tall grass, dark grass, rustling grass, walking in caves, dust clouds, and Flying Pokémon's shadows. The surfing and fishing sections aggregate Pokémon found in the water normally and those found in rippling water. The Habitat List only includes Pokémon that can be found through most random encounters; Pokémon that can only be found through swarms, gifts, and overworld interaction are not included. Version-exclusive Pokémon are only part of the Habitat List in the version in which they can appear.
Each Pokémon entry is universal. Seeing a Pokémon once anywhere (in the wild or during a Trainer battle) automatically registers it to every area that Pokémon can be found. Similarly, once a Pokémon is acquired by any means (caught, traded), every area automatically registers that Pokémon as caught for its entry.
When the player has seen all Pokémon available in the field, surfing, or fishing sections of an area, that section's tab will be decorated with a gray icon of a Poké Ball and its page will be stamped with a hollow Poké Ball outline. After the player catches every Pokémon available in a section, an exclamation mark will appear on the tab to notify the player that the section has been completed; once checked, the stamp on the page will become red and the exclamation point becomes a red and white-colored Poké Ball icon. When a player has caught every Pokémon available in all three sections of an area, that area's name on the list of areas will be decorated with a large gray shadow resembling a Poké Ball.
Rewards for completing the Habitat List
The following items are received if the player talks to a particular NPC after completing an area's section of the Habitat List:
The following areas appear in the Habitat List, but do not have any rewards for completion: