Settlement Geography II: Urban Systems, Central Place Theory, Models of Urban Land Use, Global and Edge Cities, Segregation and Urban Poverty

Walter Christaller's Die zentralen Orte in Süddeutschland (1933) asked why settlements that supply goods and services to a surrounding area are of particular sizes and spacings. He assumed an isotropic plain — uniform in fertility, population density and purchasing power, with transport equally easy in every direction and cost proportional to distance — and consumers who buy from the nearest centre. Two concepts do the work. The threshold is the minimum population or purchasing power needed to keep a good or service in business; the range is the maximum distance people will travel to obtain it. Low-order goods (bread, vegetables) have small thresholds and short ranges; high-order goods (jewellery, specialist hospitals) have large thresholds and long ranges. Circular market areas would leave gaps or overlap, so competition packs them into hexagons, the shape nearest the circle that fills a plane completely. The result is a hierarchy: higher-order centres are fewer, larger and farther apart, and supply all lower-order goods as well — Christaller identified seven orders in southern Germany, from the Marktort up to the Landeshauptstadt.

August Lösch, in Die räumliche Ordnung der Wirtschaft (1940; English translation The Economics of Location, 1954), derived the hexagon from the economics of demand: sales fall with distance as delivered price rises, generating a demand cone, and free entry squeezes market areas into hexagons. Unlike Christaller, Lösch did not fix one k for the whole system. Each good has its own threshold and so its own net of hexagons; he took the smallest possible networks (k = 3, 4, 7, 9, 12, 13, 16, 19, 21, 25 and so on), superimposed them on a single metropolis and rotated them to make as many centres coincide as possible. The result is a landscape of six city-rich and six city-poor sectors radiating from the metropolis, and a more continuous hierarchy in which centres of the same size need not offer the same functions. Christaller's model is a deductive hierarchy of fixed levels; Lösch's is a profit-maximising general equilibrium of overlapping nets.

All three are Western, industrial-city models. Their economic logic is formalised in William Alonso's bid-rent theory (1964): each land use bids a rent that falls with distance from the centre, and the use with the highest bid at each distance occupies it, producing rings. The pre-industrial city described by Gideon Sjoberg (1960) reversed the gradient, with the elite at the centre and the poor at the edge. Indian cities are usually read as dual or composite: a dense old core (walled city, bazaar and temple or mosque), a colonial layer of civil lines, cantonment and railway colony, and post-independence planned sectors, industrial estates and peripheral informal settlements.

A megacity is, in UN usage, an urban agglomeration of 10 million or more. A global (world) city is defined by function, not size: John Friedmann's world city hypothesis (1986) ranked cities as control points of the world economy, and Saskia Sassen's The Global City (1991) argued that New York, London and Tokyo had become command centres where advanced producer services — finance, law, accounting, advertising — coordinate a dispersed global production system. An edge city, in Joel Garreau's Edge City (1991), is a new concentration of offices and retail on the periphery of a metropolis: at least five million square feet of office space, more jobs than bedrooms, perceived as one place, and nothing like a city thirty years earlier — Gurugram beside Delhi is often cited as an Indian case. Around cities, the rural–urban fringe mixes farmland with urban uses; the wider peri-urban zone is functionally tied to the city while administratively rural. Suburbs are residential extensions dependent on the core; ring towns form a circle of settlements around a metropolis; satellite towns are planned, partly self-contained towns with their own employment, set beyond a green belt — the idea descends from Ebenezer Howard's garden city (1898).

Social segregation is the spatial separation of groups by class, caste, ethnicity or religion; it is measured by the index of dissimilarity, D = ½ Σ |aᵢ/A − bᵢ/B| × 100, the percentage of one group that would have to move for the two to be evenly distributed. Urban social area analysis was developed by Eshref Shevky with Marilyn Williams (1949, Los Angeles) and Wendell Bell (1955, San Francisco). From census tract data it built three indices — social rank (economic status: occupation and education), urbanisation (family status: fertility, women in the labour force, single-family dwellings) and segregation (ethnic status). Later factorial ecology derived the dimensions statistically, and Robert Murdie (1969) showed that they map onto the classical models: economic status varies by sectors (Hoyt), family status by concentric zones (Burgess), and ethnic status in clusters (multiple nuclei).

Poverty in the city takes four forms named in the document. Slums — the 2011 census counted about 65 million people in slums, in statutory towns that reported them. The informal sector — a term popularised by Keith Hart's study of Accra (1973) and the ILO's Kenya mission report (1972) — covers unregistered, unprotected work such as street vending, domestic service and home-based manufacture, and employs the majority of urban workers in India. Crime tends to concentrate where poverty, overcrowding and weak institutions coincide. Social exclusion is the denial of full participation in society through lack of housing tenure, identity documents, services and voice; Oscar Lewis's idea of a self-perpetuating "culture of poverty" (1959, 1966) has been widely criticised for blaming the poor for structural conditions.