cardinal directions into their street numbers, so that in many such cities, addresses roughly follow a Cartesian coordinate system. Some other cities around the world have their own schemes. Although house numbering is the principal identification scheme in many parts of the world, it is also common for houses in the United Kingdom and Ireland to be identified by name, rather than number, especially in villages. In these cases, the street name will usually follow the house name. Such an address might read: "Smith Cottage, Frog Lane, Barchester, Barsetshire, BZ9 9BA" or "Dunroamin, Emo, Co. Laois, Ireland" (fictional examples). Quadrants In cities with Cartesian-coordinate-based addressing systems, the streets that form the north–south and east–west dividing lines constitute the x and y axes of a Cartesian coordinate plane and thus divide the city into quadrants. The quadrants are typically identified in the street names, although the manner of doing so varies from city to city. For example, in one city, all streets in the northeast quadrant may have "NE" prefixed or suffixed to their street names, while in another, the intersection of North Calvert Street and East 27th Street can be only in the northeast quadrant. Street-naming conventions Street names may follow a variety of themes. In many North American cities, such as San Francisco, USA, and Edmonton, Alberta and Vancouver, British Columbia, streets are simply numbered sequentially across the street grid. Numbered streets originated in the United States in Philadelphia by Thomas Holme who laid out the original plan for the city in 1683. Washington, D.C. has its numbered streets running north–south and lettered or alphabetically named streets running east–west, while diagonal avenues are typically named after states. In Salt Lake City, and many other Utah cities, streets are in a large grid and are numbered in increments of 100 based on their location relative to the center of the city in blocks. A similar system is in use in Detroit with the Mile Road System. In some housing developments in North America and elsewhere, street names may all follow the same theme (for example, bird species), or start with the same letter. Streets in Continental Europe, the Middle East, and Latin America are often named after famous people or significant dates. Postal codes Postal codes are a relatively recent development in addressing, designed to speed the sorting and processing of mail by assigning unique numeric or alphanumeric codes to