The street layout of Seattle is based on a series of disjointed rectangular street grids. Most of Seattle and King County use a single street grid, oriented on true north. Near the center of the city, various land claims were platted in the 19th century with differently oriented grids, which still survive today. Distinctly oriented grids also exist in some cities annexed by Seattle in the early 20th century, such as Ballard and Georgetown. A small number of streets and roads are exceptions to the grid pattern.