Nigerian urbanism, as in other parts of the world, is a function primarily of trade and politics. In the north, the great urban centers of Kano, Katsina, Zaria, Sokoto, the early Borno capitals (Gazargamo and Kuka), and other cities served as entrepôts to the Saharan and trans-Saharan trade, and as central citadels and political capitals for the expanding states of the northern savanna. They attracted large numbers of traders and migrants from their own hinterlands and generally also included "stranger quarters" for migrants of other regions and nations. In the south, the rise of the Yoruba expansionist city-states and of Benin and others was stimulated by trade to the coast, and by competition among these growing urban centers for the control of their hinterlands and of the trade from the interior to the Atlantic (including the slave trade). The activities of European traders also attracted people to such coastal cities as Lagos, Badagri, Brass, and Bonny, and later Calabar and Port Harcourt. Overlying the original features of the earlier cities were those generated by colonial and postcolonial rule, which created new urban centers while also drastically altering the older ones. All these cities and peri-urban areas generally tended to have high population densities.

The northern savanna cities grew within city walls, at the center of which were the main market, government buildings, and the central mosque. Around them clustered the houses of the rich and powerful. Smaller markets and denser housing were found away from this core, along with little markets at the gates and some cleared land within the gates that was needed especially for siege agriculture. Groups of specialized craft manufacturers (cloth dyers, weavers, potters, and the like) were organized into special quarters, the enterprises often being family-based and inherited. Roads from the gates ran into the central market and the administrative headquarters. Cemeteries were outside the city gates.

The concentration of wealth, prestige, political power, and religious learning in the cities attracted large numbers of migrants, both from the neighboring countryside and from distant regions. This influx occasioned the building of additional sections of the city to accommodate these strangers. In many of the northern cities, these areas were separated between sections for the distant, often non-Muslim migrants not subject to the religious and other prohibitions of the emir, and for those who came from the local region and were subjects of the emir. The former area was designated the "Sabon Gari," or new town (which in southern cities, such as Ibadan, has often been shortened to "Sabo"), while the latter was often known as the "Tudun Wada," an area often quite wealthy and elaborately laid out. To the precolonial sections of the town was often added a government area for expatriate administrators. The result was that many of the northern cities have grown from a single centralized core to being polynucleated cities, with areas whose distinctive character reflected their origins, and the roles and posit 1000 tion of their inhabitants.

Surrounding many of the large, older northern cities, including Kano, Sokoto, and Katsina, there developed regions of relatively dense rural settlement where increasingly intensive agriculture was practiced to supply food and other products to the urban population. These areas have come to be known as close settled zones, and they were of major importance to the agricultural economies of the north. By 1990 the inner close settled zone around Kano, and the largest of its kind, extended to a radius of about thirty kilometers, essentially the limit of a day trip to the city on foot or by donkey. Within this inner zone, there has long been a tradition of intensive interaction between the rural and urban populations, involving not just food but also wood for fuel, manure, and a range of trade goods. There has also been much land investment and speculation in this zone. The full range of Kano's outer close settled zone in 1990 was considered to extend sixty-five to ninety-five kilometers from the city, and the rural-urban interactions had extended in distance and increased in intensity because of the great improvements in roads and in the availability of motorized transport. Within this zone, the great majority of usable land was under annual rainy season or continuous irrigated cultivation, making it one of the most intensively cultivated regions in sub-Saharan Africa.

In the south, there were some similarities of origin and design in the forest and southern savanna cities of Yorubaland, but culture, landscape, and history generated a very different character for most of these cities. As in the north, the earlier Yoruba towns often centered around the palace of a ruler, or afin, which was surrounded by a large open space and a market. This arrangement was still evident in older cities such as Ife. However, many of the most important contemporary Yoruba cities, including the largest, Ibadan, were founded during the period of the Yoruba wars in the first half of the nineteenth century. Reflecting their origins as war camps, they usually contained multiple centers of power without a single central palace. Instead, the main market often assumed the central position in the original town, and there were several separate areas of important compounds established by the major original factions. Abeokuta, for example, had three main chiefly families from the Egba clan who had broken away from and become important rivals of Ibadan. Besides these divisions were the separate areas built for stranger migrants, such as Sabo in Ibadan, where many of the Hausa migrants resided the sections added during the colonial era, often as government reserve areas (GRAs) and the numerous areas of postcolonial expansion, generally having little or no planning.

The high population densities typically found in Yoruba cities--and even in rural villages in Yorubaland--were among the striking features of the region. This culturally based pattern was probably reinforced during the period of intense intercity warfare, but it persisted in most areas through the colonial and independence periods. The distinctive Yoruba pattern of densification involved filling in compounds with additional rooms, then adding a second, third, or sometimes even a fourth story. Eventually, hundreds of people might live in a space that had been occupied by only one extended family two or three generations earlier. Fueling this process of densification were the close connections between rural and urban dwellers, and the tendency for any Yoruba who could afford it to maintain both urban and rural residences.

The colonial government, in addition to adding sections to existing cities, also created important new urban centers in areas where there previously had been none. Among the most important were Kaduna, the colonial capital of the Protectorate of Northern Nigeria, and Jos in the central highlands, which was the center of the tin mining industry on the plateau and a recreational town for expatriates and the Nigerian elite. These new c 8caities lalacked walls but had centrally located administrative buildings and major road and rail transport routes, along which the main markets developed. These routes became one of the main forces for the cities' growth. The result was usually a basically linear city, rather than the circular pattern largely based on defensive needs, which characterized the earlier indigenous urban centers.

The other ubiquitous colonial addition was the segregated GRA, consisting of European-style housing, a hospital or nursing station, and educational, recreational, and religious facilities for the British colonials and the more prominent European trading community. The whole formed an expatriate enclave, which was deliberately separated from the indigenous Nigerian areas, ostensibly to control sanitation and limit the spread of diseases such as malaria. After independence, these areas generally became upper income suburbs, which sometimes spread outward into surrounding farmlands as well as inward to fill in the space that formerly separated the GRA from the rest of the city. New institutions, such as university campuses, government office complexes, hospitals, and hotels, were often located outside or on the fringes of the city in the 1980s. The space that originally separated them from the denser areas was then filled in as further growth occurred.

Data as of June 1991