A new exhibit opens at MoMA tomorrow. Called Uneven Growth: Tactical Urbanisms for Growing Megacities, it looks at how urban planners could work informal housing developments to make megacities more livable.

This is an imagined view of Lagos, Nigeria, in 2050. Thirty percent of Lagos is currently underwater, leading to "water slum" housing, and the roads are congested with SUVs. Architects propose embracing the water to create transportation and economic opportunity, like in Venice or Amsterdam.

By transforming existing infrastructure, like gas generators, into architecture for renewable energy, Lagos would go off the grid.

Hong Kong's population is growing fast, but the city is mostly surrounded by water. Architects propose building eight new islands off the coast, each one dedicated to an economic activity. This one is the island of surplus, where waste gets sent for future use.

Istanbul's middle class aspires to live in TOKIs, gated communities where everyone owns a car, many gadgets, and could soon be in debt. This rendering shows what TOKIs could be like if they turn into new-age communes and embracing car, compost, and service sharing, along with solar panels and local gardens.

Almost 12 million of Mumbai's residents live in informal "tool houses," slum-like structures where people live and work. Rather than razing these for high-rises, architects propose validating them.

Part of the proposal includes investing and developing new lightweight construction materials to allow ad-hoc spaces to be built safely.

Luxury developments have created a housing shortage for many New Yorkers. That leads to rent burden and illegally subdivided apartments. Housing Cooperative Trusts are proposed here, in which the city, non-profits, community stakeholders, and tenants would all co-own rehabilitated buildings and ensure long-term affordable housing.

Community Growth Organizations would also form, to turn underutilized spaces—like yards and rooftops—into pockets of economic activity. (To be fair, this type of local urban planning is already underway in New York.)

Rio is well known for its favelas. The urban planners for this project decided to create a new consumer catalog that encourages people to build add-ons.

That catalog would be called Veranda Products. By selling consumer goods that make ad-hoc building easier, the city could foster small-scale entrepreneurial projects, and therefore give poorer cariocas access to more economic activity.