A wharf is a laning place or pier where ships may tie up and load or unload. A wharf is a fixed platform, commonly on pilings. They often serve as interim storage areas with warehouses, since the typical objective is to unload and reload vessels as quickly as possible. Where capacity is sufficient a single quay constructed along the land adjacent to the water is normally used; where there is a need for more capacity many wharves will instead be constructed projecting into the water, as with the well known collection of wharves in San Francisco. A pier, raised over the water rather than within it, is one type of wharf, commonly used for cases where the weight or volume of cargos will be low.