Street-network Sprawl in Sousse, Tunisia

What is Street-network sprawl?

Street-network Sprawl is a way to measure urban sprawl, worldwide, through the connectedness of the streets. Less sprawl means more connected, more walkable streets. Well-connected streets – like New York City’s grid – are more walkable and can be served by public transit.

The street network is permanent, and its connectivity affects the livability and environmental footprint of cities for decades and centuries to come. In places with more connected streets, residents drive less and walk more. A well-connected street network is associated with better outcomes for health, the environment, sustainable consumption, social integration, and equity.

We can quantify how connected street networks are with the Street Network Disconnectedness Index (SNDi).

SNDi -- our measure of street-network sprawl (disconnectedness)

The SNDi is a comprehensive measurement of “sprawl”. It captures:

A higher SNDi means less-connected streets – i.e., more sprawl. For the 10137 cities in our dataset, the average SNDi is 2.25, with half of the cities' SNDis falling between 1.08 and 3.25.

More information on the sprawl index can be found in these research papers:

To see the state of street-network sprawl across the globe, visit the sprawlmap.

Sousse: region in Tunisia

What exactly constitutes the spatial extent of the city? For these aggregations, we used the Global Human Settlement Layer Urban Center Database (GHS-UCDB) to define the boundaries of the city. These cities -- or urban centers -- cover areas that are densely populated and built-up, and so may extend beyond the spatial borders of these cities that we may be familiar with. The GHS area is shaded in blue.

View Sousse, Tunisia on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Sousse as of 2014, the overall level of street-network sprawl is 1.36, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 1.45, 1.3, 1.27 and 2.26. The disconnectivity of new streets constructed in Sousse fell, then rose. In 1991-2000, new street layouts were the most connected.

Quantity of street network construction: The street network in Sousse spans a total of 3271 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 1.3, which is relatively well-connected.

Effect on the aggregate network: New construction in each period adds to the total stock of streets, but does not change streets that have already been built. Therefore, it has a limited effect on the street network as a whole. The SNDis of the aggregate street network in the respective time periods are 1.45, 1.31, 1.29 and 1.36. The SNDi of the aggregate street network in fell at first, but Sousse has worsened in disconnectivity since 2000.

The level of street-network sprawl in new development in Sousse was at its lowest in 1991-2000. To get a sense of how street development has changed in Sousse, we can consider two of its most populous cities: Sousse and M'Saken. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Sousse followed a zig-zag trend with an overall increase. The level of street-network sprawl in new development in M'Saken was at its lowest in 1976-1990.

How do development practices in Sousse fare in comparison to others in Tunisia? Most recently in 2001-2014, street construction in Sousse was the 12th-most disconnected out of the 18 regions in Tunisia. Its position in the ranks since 1975 has not changed. Sousse ranked 12th in 1975, 15th in 1976-1990, 17th in 1991-2000 and 12th in 2001-2014.

As of 2014, the city with the most disconnected street network in Sousse is M'Saken with an SNDi of 1.74, which is relatively well-connected. Conversely, the most connected city is Sousse with an SNDi of 1.1, which is relatively well-connected. See trends for these cities: Sousse, M'Saken

The level of street-network sprawl in the aggregate network in Sousse was at its lowest in 1991-2000. To get a sense of how the aggregate street network has changed in Sousse, we can consider two of its most populous cities: Sousse and M'Saken. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Sousse followed a zig-zag trend with an overall increase. The level of street-network sprawl in the aggregate network in M'Saken was at its lowest in 1976-1990.

To date, Sousse is the 16th-most disconnected out of the 18 regions in Tunisia. Its position in the ranks since 1975 has fallen; relative to other regions in Tunisia, the street network in Sousse has become more connected. Sousse ranked 12th in 1975, 16th in 1976-1990, 16th in 1991-2000 and 16th in 2001-2014.