Johannesburg Looks Ahead: The City Growth Modelling Project

Like many African cities, Johannesburg is growing faster than it can plan for. South Africa's economic hub and home to more than six million people, the city is expanding both formally and informally while population density, infrastructure provision, and rates collection remain unevenly distributed. Urbanisation is outpacing economic growth for residents and municipality alike. Housing is unaffordable. Informal settlements are spreading. Services can't keep pace. The city must invest billions in the years ahead, and the wrong choices could lock residents into spatial exclusion for generations.

The traditional response to this kind of pressure is reactive: build where demand is loudest, spend where politics points, and hope the pieces cohere. Johannesburg is attempting something different.

Thinking in Futures

Through the Joburg 2040 Growth and Development Strategy (GDS), the city has committed to long-term, adaptive governance — treating uncertainty as a starting point rather than an excuse for short-termism. The GDS sets out an ambitious vision: an economically vibrant, inclusive, low-carbon city that provides high-quality services for all its citizens. But vision documents are only as useful as the tools that translate them into decisions.

That's where the City Growth Modelling project comes in. Developed over three years in partnership with the Council for Scientific and Industrial Research (CSIR), the model doesn't predict the future — it tests alternatives. By modelling various development scenarios over a 20-year horizon, it allows planners to ask: if we invest here, and density grows there, what happens to infrastructure demand, access to jobs, and municipal finances?

What the Model Revealed

When modellers compared a trend-based growth path (peripheral expansion, informality) against one aligned with the city's Spatial Development Framework (SDF), the SDF-aligned scenario demonstrated significantly improved outcomes compared to the trend path: lower informality, closer alignment between jobs and housing, and more practical and affordable infrastructure requirements. Crucially, improved job access under this scenario came from densifying existing formal developments — rather than upgrading outlying or underserved areas. That's a finding with direct implications for where the city should focus investment.

Surfacing Difficult Trade-offs

The model also showed something harder to hear. When the growth model was overlaid with the city's own revenue mapping, a clear tension emerged: some areas receiving substantial social investment were unlikely to generate jobs or municipal revenue in the medium and possibly even long term. Well-intentioned spending, the data suggested, could quietly undermine the city's financial resilience.

Rather than leaving this as a political flashpoint, foresight created a structured, analytical space to examine the trade off, allowing the conversation to shift towards balancing social and financial returns, and making a case for redirecting investment toward inclusive densification in areas that already show economic potential.

In another example, when detailed revenue modelling proved too complex to deliver in full, the team pivoted to a social facility gap analysis — itself a foresight outcome worth noting. By mapping where future population growth would outstrip access to clinics and schools, the project could estimate long-term spending requirements and prioritise investment where it would have the greatest impact on quality of life.

From Insight to Infrastructure

Strategic foresight is most valuable when insights turn to implementation. In Johannesburg's case, the city recently approved its Infrastructure Plan 1.0, including a Capital Expenditure Framework that directly incorporates the modelling outcomes. Foresight has moved from the whiteboard into influencing concrete investment decisions.

A model that treats cities as complex, interdependent systems rather than collections of problems to be solved in sequence. By building futures thinking into everyday planning practice, Johannesburg can navigate a surer path through the uncertainty that the future brings.

The pressures facing Johannesburg — rapid urbanisation, deep inequality, constrained municipal finances — are not unique to South Africa. They are the defining conditions of urban growth across much of the global south. What makes this case compelling is the insistence that cities can, and must, plan their way through them — not by predicting what comes next, but by understanding what today's decisions make possible.