By 2050, close to two-thirds of humanity will live in cities, according to the United Nations; more than half already does. That growth is concentrated in countries short of the time and the means to plan for it. Macky Sall wants urbanisation there to become an engine of development, and he has made it one of the commitments of his candidacy for the office of UN Secretary-General.

Growth that outruns services. Cities grow faster than their water networks and their schools. On the outskirts of Lagos or Kinshasa, a family buys a plot before any street reaches it, then waits years for a connection. About one billion people today live in precarious neighbourhoods, without title deeds or sanitation. A city that spreads before it is equipped manufactures poverty at the pace it gains inhabitants.

The place where the climate is decided. Cities produce the largest share of global emissions, through their transport and their buildings. They are also where those emissions fall fastest, when a public transport network replaces thousands of individual journeys and a well-designed building consumes half as much.

Planning before suffering. Reserving land and laying out transport and housing before residents arrive costs far less than catching up afterwards. The countries that planned their cities turned them into engines of growth; those that let them grow alone pay the price every year.

What the Secretariat can carry. The Secretary-General can support the United Nations Human Settlements Programme, based in Nairobi, and keep the city on the agenda of development conferences. Urban plans remain the business of states and municipalities. The Secretariat's voice counts for what a mayor often decides too late, the layout of networks and the reserve of land, before the residents move in.

Experience in multilateral negotiation. Twelve years as head of state and the chairmanship of the African Union in 2022 underpin these commitments. That experience explains why the vision statement filed with the United Nations frames its proposals as obligations: peace, security and development conceived together; a renewed multilateralism; stronger governance of the Organization.

Africa at its heart, the world in its sights.

The United Nations' projections on world urbanisation and Sustainable Development Goal 11 are public. Read all public positions at www.mackysall.net