Several types of closed areas, including Rockfish Conservation Areas, or RCAs, and Block Area Closures, or BACs, are closed areas that are at least partially defined by depth-based boundary lines. Depth-based boundaries are lines that connect a series of latitude and longitude coordinates and are intended to approximate particular depth contours. These boundary lines are typically defined coast-wide and around islands, with a few exceptions, but may be used to define a closed area off just a part of the coast.