A city in the desert. Without water. The only example I can think of that I’ve been to is Las Vegas, but even it draws its water from the nearby Colorado River. There are no true desert cities on Earth.
But would a desert city be possible? The Sahara and Gobi deserts in Africa and Asia, respectively, take up an immense amount of land area that could otherwise be used for human civilization. Obviously, no one is going to throw up a megalopolis in either place anytime soon, and neither region’s surrounding land currently has any water to spare, but what about in the future?
I think the solution for the desert conundrum can actually be found in another place far away: Mars. Mars has significantly less water than even the driest of Earthen deserts, yet humanity still strives to conquer it. Scientists have recently found evidence of flowing, liquid water on Mars, but this does not occur in a consistent manner or in suitable quantities for sustained Martian civilization.
Instead, Martian water will likely come from ice in the ground and be recycled meticulously to preserve every last drop for future Martian colonists. I think a similar system of careful water recycling could be implemented on Earth to create future desert cities. Plants could be genetically engineered to require less water. Buildings could be built underground in the sand dunes to retain most of the moisture within the environment.
These cities would be physically self-sustaining and be able to bar themselves off from the outside world if they pleased (in case of a global pandemic, for example), but they could also be connected to the outside world by vast desert highways, and airports could be built with all of the space the desert provides to give easy access to the more populated areas outside the desert.
And, of course, these desert communities could have access to the rest of the Earth with the internet. I imagine their economies would either be subsistanc-based or highly information-based, so the internet would be imperative.
As humanity progresses, cities will grow. The UN projects the world population to reach 11 billion by 2100. I personally believe this is an underestimation, but even adding just 4 billion more people would place a massive burden on existing infrastructures. Already-crowded countries like India, Bangladesh, and Nigeria are expected to take on the majority of this population growth, and those countries likely could not handle such an increase. I think a diaspora will take place in the future as overcrowded countries crumble from overpopulation, and their peoples will need places to live. The desert is one such place where people could build new communities without overpopulating existing ones.