Street-network Sprawl in Ouaddaï, Chad

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.

Ouaddaï: region in Chad

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 Ouaddaï, Chad on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Ouaddaï as of 2014, the overall level of street-network sprawl is 2.74, which is in the 40th to 60th percentile of disconnectedness.

Trends in street network construction: The SNDis of street construction for the respective time periods are 0.51, nan, nan and 2.07. Data was not available in 1976-1990 and 1991-2000.

Quantity of street network construction: The street network in Ouaddaï spans a total of 1245 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 2.07, 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 0.51, 5.08, 5.08 and 2.74. The aggregate street network in Ouaddaï increased in disconnectivity initially,but the trend has turned around after 1990.

The level of street-network sprawl in new development in Ouaddaï followed a zig-zag trend with an overall increase. To get a sense of how street development has changed in Ouaddaï, we can consider two of its most populous cities: Abéché and أدري Adré. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Abéché followed a zig-zag trend. The level of street-network sprawl in new development in أدري Adré followed a zig-zag trend with an overall decrease.

How do development practices in Ouaddaï fare in comparison to others in Chad? Most recently in 2001-2014, street construction in Ouaddaï was the 7th-most disconnected out of the 17 regions in Chad. Ouaddaï ranked 5th in 1975 and 7th in 2001-2014. There was no ranking in 1976-1990 and 1991-2000 due to unavailable data.

As of 2014, the city with the most disconnected street network in Ouaddaï is Abéché with an SNDi of 0.64, which is relatively well-connected. Conversely, the most connected city is أدري Adré with an SNDi of -0.42, which is very well-connected. See trends for these cities: أدري Adré, Abéché

The level of street-network sprawl in the aggregate network in Ouaddaï peaked in 1976-1990. To get a sense of how the aggregate street network has changed in Ouaddaï, we can consider two of its most populous cities: Abéché and أدري Adré. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Abéché followed a zig-zag trend. The level of street-network sprawl in the aggregate network in أدري Adré fell steadily.

To date, Ouaddaï is the 7th-most disconnected out of the 17 regions in Chad. Its position in the ranks since 1975 has fallen; relative to other regions in Chad, the street network in Ouaddaï has become more connected. Ouaddaï ranked 5th in 1975, 3rd in 1976-1990, 2nd in 1991-2000 and 7th in 2001-2014.