THIS PAST AUGUST IN HELIOPOLIS, the Cairo suburb built over desert by a Belgian industrialist in 1905, I sat in an architect's office, a place called Cube Architectural Consultants, and heard a glowing, impromptu presentation on "Cairo 2050." Cairo 2050 is a series of outlandish master plans and megaprojects for Egypt's capital that the regime of Hosni Mubarak began promoting in 2008, with the help of the United Nations and the Japanese government. Its future, an earnest architect informed me gently, was "uncertain in the new Egypt."

Imagine Dubai in the Nile Valley, if instead of building it on empty sand, futurist skyscrapers and business parks rose over what are now the packed, informal neighborhoods that today house the majority of Cairo's estimated 17 million people. This authoritarian, outsized development "vision" would involve relocating millions to the furthest edges of the desert - areas banally termed "new housing extensions" - to make way for "10 star" hotels, huge parks, "residential touristic compounds," and landing-strip-sized boulevards lined with a monotony of towers. It's unlikely to happen in an Egypt after Mubarak - if it was ever possible at all, given budgets and popular resistance. Still, Cairo 2050 offers a glimpse at the Egyptian government's approach to urban planning and policy. As David Sims, an economist and consultant who has worked in Cairo since 1974, writes in Understanding Cairo: The Logic of a City Out of Control, the Cairo 2050 project represents "a continued penchant for the manufacture of unrealistic dreams" on the part of "government planners and their consultants."

Sims is one of Cairo's sharpest observers. He was one of the first scholars to study Cairo's informal areas - large and expanding "extralegal" neighborhoods, as he defines them, that were built without planning or permits mostly on once private, reclaimed agricultural land. They began to proliferate in the 1970s, largely funded by remittances sent home by Egyptian men laboring in the oil-boom Gulf. The informal areas have come to dominate the city's urban fabric, yet are known pejoratively in Cairo as 'ashwa'i areas or 'ashwaiyyat ("random" or "haphazard" in Arabic), condemned by the government and the well-to-do as vast slums, as home to rural migrants unable to adapt to the city life, and, beginning in the 1990s, as havens for Islamist militants. Which isn't to say the government has no presence in informal areas. Corrupt urban bureaucracy tacitly accepted their expansion, making access to basic municipal services and infrastructure a matter of bribes and clientelism. Often described in monolithic if shadowy terms, many informal areas are left off maps of the city altogether. Yet Sims shows that they demonstrate great adaptability, with a variety of building types and a vernacular order mimicking the patterns of medieval Cairo, with their density, their compact plots, and their narrow, meandering streets.

Cairo 2050 was the government's response to this rapid, informal urbanization. The scheme promised residents of informal areas a new "civilized residential environment" miles away in the desert, while their old neighborhoods, like the areas in Giza near the pyramids, would become luxury centers of tourism and business. You might call Cairo 2050 useful, then, not for grasping some imaginary future, but for understanding the city's recent development - and for deepening our underst...