No one has documented the changing geography of low‐income settlements in any city in the developing world over the entire postwar period. The most plausible model of this changing geography, first outlined by John F.C. Turner, indicates the existence of a dual concentration of the poor: in central slums and in informal settlements at the periphery. This dual pattern is associated, respectively, with the filtering‐down of older housing and with owner‐construction of new dwellings, sometimes on illegally‐occupied land. Some writers have suggested that central slums deteriorate, while fringe settlements may be improved over time, thereby distinguishing slums of despair from those of hope. Analysis of the Egyptian census from 1947 to 1996 shows that this suggestion is borne out by the postwar experience of Cairo. Evidence on literacy indicates that central and fringe areas have both contained a high proportion of low‐income households, but that over half a century the relative status of the central areas has slowly declined. Although it has helped to shape the experience of millions, this long‐term trend has not been obvious to close observers of the local scene. Similar historical surveys should be undertaken of low‐income settlements in other cities in the developing world.