Making room for urban expansion matters because it ensures a supply of developable land, both in the existing city and in new areas, that is sufficient to keep housing affordable for the urban poor. It also matters because it allows the city to guide development, rather than follow it. By leading, rather than following development, cities can greatly reduce the cost of providing infrastructure and public open spaces, ensuring that all urban residents have access.

We believe that the making-room approach—through densification and orderly, climate-sensitive expansion—is the way to create cities that are more equitable, efficient, livable, and sustainable.

The making-room approach calls for innovation, by combining data and policy recommendations, in accommodating future growth in the existing city or in new developments.

To accommodate growth in the existing city through affordable densification, we must understand the anatomy of density. A measure of densification capacity is generated along with specific policy recommendations to achieve such density.

To accommodate growth in new areas, we recommend four key steps:

• First, make realistic projections, both about the amount of land that the growing urban population will require and where the physical expansion of the city is likely to take place.
• Second, cities should work with regional and national officials to ensure that they obtain jurisdiction over the projected area of expansion.
• Third, carry out basic urban planning in the area of expansion. The city will have to establish rights of way for a network of arterial roads—roads that will one day carry public transit and private traffic as well as infrastructure such as water mains, sewers and storm sewers, and telecommunications networks.
• Finally, the city should identify public open spaces, including environmentally sensitive areas, and work to protect them in the face of urban development.

To date, we have completed two national initiatives, with Ethiopia and Colombia. In both countries, a number of cities finalized their plans for the infrastructure grid areas and secured the rights-of-way in their expansion areas for a grid of 30-meter-wide arterial roads, spaced one kilometer apart. What’s more, national authorities in both countries worked with us to expand the initiative to more of their fast-growing cities and created national programs. All details can be found in the description of each project, along with the anatomy-of-density study results.