From Nookipedia, the Animal Crossing wiki
Rover telling the player about transferring over data from Wild World

When creating a new character in Animal Crossing: City Folk, Rover gives the player the option to transfer over a Animal Crossing: Wild World character. When a Wild World character is transferred, the new City Folk character will retain the player's name, eyes, face, and hairstyle. Most of the player's catalog will also transfer over, excluding collectibles such as fossils and Gyroids.

Some items such as the Miniature Car and some stationery are only obtainable in City Folk through the catalog after a transfer has been made.