Spatial structure and efficiency of commuting in Senegalese cities

Session 4: National Statistics International audience Senegal is experiencing an unprecedented urban revolution: according to the latest UN projections, its urban population will be multiplied by 3 in the forthcoming decades, to reach 18 million people by 2050. While cities are often lauded as the solution to mankind's socio-economical and environmental issues, when badly managed, they can also be recipes for disasters. In order to propose well-informed transport and planning policies in Senegal, it is crucial to first measure and understand the key spatial dynamics that shape its cities. In this report, we uncover commuting patterns in the 12 largest urban areas of Senegal and their coarse-grained spatial properties using mobile phone data, allowing us to characterize the efficiency of commuting and to compare cities with each other. At the inter-urban level, we show that for most cities, the vast majority of commuters live and work in the same urban area, meaning that Senegalese cities are well-integrated employment markets. We then compute the geographical area of influence of each city. This confirms the importance of large cities such as Dakar, but also highlights smaller cities which play an important economical role such as Tambacounda or Touba. At the intra-urban level, we quantity the spatial mismatch between residence and workplace locations and we propose a measure of the 'optimality' of the commuting structure. We find that Dakar, with a high optimality index, has a coherent spatial structure with nested residential and employment areas which is reflected in the fact that 80% of the residential and activity hostspots overlap. Smaller cities however-such as Louga, Kolda, Mbour-are far from the optimal commuting solution. The methods proposed in this study could help urban planners in identifying locations and areas which are the most penalized by inefficient commuting, a source of economic loss and stress on people's life and the environment.