Street-network Sprawl in Sangha-Mbaéré, Central African Republic

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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:

• nodal degree
• dendricity, the tree-likeness of the street network
• circuity, the ratio of the distance by road to the straight-line distance of two locations on the street network
• sinuosity, the curviness of a street

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:

• Global trends toward urban street-network sprawl
• A global assessment of street-network sprawl

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

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Sangha-Mbaéré: region in Central African Republic

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 Sangha-Mbaéré, Central African Republic on the sprawlmap

How have Sangha-Mbaéré's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Sangha-Mbaéré as of 2014, the overall level of street-network sprawl is 5.31, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 4.6, 5.17, 4.39 and 7.42. Disconnectivity in street construction in Sangha-Mbaéré follows a zig-zag trend. In 1991-2000, street construction was most disconnected, while construction was most connected in 2001-2014.

Quantity of street network construction: The street network in Sangha-Mbaéré spans a total of 792 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 5.17, which is highly disconnected.

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 4.6, 5.1, 4.93 and 5.31. Disconnectivity in Sangha-Mbaéré's street network follows a zig-zag trend. In 1975, the region was most disconnected; while it was most connected in 2001-2014.

Sangha-Mbaéré in context: Street-network sprawl of new development

The level of street-network sprawl in new development in Sangha-Mbaéré followed a zig-zag trend with an overall increase. To get a sense of how street development has changed in Sangha-Mbaéré, we can consider one of its most populous cities: Nola. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Nola followed a zig-zag trend.

How do development practices in Sangha-Mbaéré fare in comparison to others in Central African Republic? Most recently in 2001-2014, street construction in Sangha-Mbaéré was the 1st-most disconnected out of the 6 regions in Central African Republic. Its position in the ranks since 1975 has not changed. Sangha-Mbaéré ranked 1st in 1975, 2nd in 1976-1990, 4th in 1991-2000 and 1st in 2001-2014.

Sangha-Mbaéré in context: Aggregate street-network sprawl

As of 2014, the city with the most disconnected street network in Sangha-Mbaéré is Nola with an SNDi of 1.12, which is relatively well-connected. Conversely, the most connected city is Nola with an SNDi of 1.12, which is relatively well-connected. See trends for these cities: Nola, Nola

The level of street-network sprawl in the aggregate network in Sangha-Mbaéré followed a zig-zag trend with an overall increase. To get a sense of how the aggregate street network has changed in Sangha-Mbaéré, we can consider one of its most populous cities: Nola. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Nola rose steadily.

To date, Sangha-Mbaéré is the 1st-most disconnected out of the 6 regions in Central African Republic. Its position in the ranks since 1975 has not changed. Sangha-Mbaéré ranked 1st in 1975, 2nd in 1976-1990, 2nd in 1991-2000 and 1st in 2001-2014.

Cities in Sangha-Mbaéré

• Nola