Settlement hierarchy  A settlement hierarchy is a way of arranging settlements into a hierarchy based upon their population or some other criteria. The term is used by landscape historians and in the National Curriculum for England. The term is also used in the planning system for the UK and for some other countries such as Ireland, India and Switzerland. The term was used without comment by the geographer Brian Roberts in 1972. Throughout human history there was a hard limit on settlement density, as walking distance influenced geography; people simply were unwilling to live or work farther than 5 miles (or 10 if they owned a horse) from the nearest town to obtain everyday basic goods and services. In Europe, centuries-old settlements were surrounded by farmland and tended not to be wider than 30 minutes' walk from one end to the other, with wealthier people monopolizing the "town center", while poorer people lived on the town's outskirts or nearby countryside (the "sphere of influence"). With the advent of decentralization technologies (i.e., bicycles, trains, cars, etc.), American settlements reversed this trend before reaching their saturation point, with vast farmlands managed by homesteads located dozens of miles away from the nearest settlement; lower-income communities occupied the "center" as the middle-income and upper-income migrated into suburbia, and this created a phenomenon known as urban decay. A settlement's population size, its geographic area, its status and the availability of services can all affect this hierarchy. Position in a settlement hierarchy can also depend on the sphere of influence. This is how far people will travel to use the services in the settlement: if people travel further the town becomes more important and ranks higher in the settlement hierarchy. Using size of a settlement can be misleading in some cases as not all population boundaries fit. Some cities (e.g., Norwich, England) have a smaller population than some towns (e.g., Luton, England). In addition, there is no agreement as to the number of levels in the hierarchy or what they should be called. Many terms used to describe settlements (e.g., village) have no legal definition, or may have contradictory legal definitions in different jurisdictions. Position in an accepted settlement hierarchy can imply status which in turn reinforces the position of the settlement in the hierarchy. Status can derive from being the residence of a King or high-ranking member of the nobility or from being the location of a major religious establishment. A formal hierarchy of settlements, known as a multiple estate appears to have been common in 10th century England.