Street-network Sprawl in Afar, Ethiopia

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.

Afar: region in Ethiopia

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 Afar, Ethiopia on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Afar as of 2014, the overall level of street-network sprawl is 5.49, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are nan, 9.49, 1.37 and 5.54. Data was not available in 1975.

Quantity of street network construction: The street network in Afar spans a total of 2513 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 5.54, 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 nan, 9.92, 4.6 and 5.49. Data was not available in 1975.

The level of street-network sprawl in new development in Afar followed a zig-zag trend. To get a sense of how street development has changed in Afar, we can consider two of its most populous cities: Lower Miele and Asaita. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Lower Miele followed a zig-zag trend. The level of street-network sprawl in new development in Asaita followed a zig-zag trend.

How do development practices in Afar fare in comparison to others in Ethiopia? Most recently in 2001-2014, street construction in Afar was the 1st-most disconnected out of the 11 regions in Ethiopia. Its position in the ranks since 1975 has not changed. Afar ranked 1st in 1976-1990, 9th in 1991-2000 and 1st in 2001-2014. There was no ranking in 1975 due to unavailable data.

As of 2014, the city with the most disconnected street network in Afar is Asaita with an SNDi of 4.71, which is highly disconnected. Conversely, the most connected city is Lower Miele with an SNDi of -2.76, which is very well-connected. See trends for these cities: Lower Miele, Asaita

The level of street-network sprawl in the aggregate network in Afar followed a zig-zag trend. To get a sense of how the aggregate street network has changed in Afar, we can consider two of its most populous cities: Lower Miele and Asaita. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Lower Miele followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Asaita followed a zig-zag trend.

To date, Afar is the 2nd-most disconnected out of the 11 regions in Ethiopia. Its position in the ranks since 1975 has fallen; relative to other regions in Ethiopia, the street network in Afar has become more connected. Afar ranked 1st in 1976-1990, 2nd in 1991-2000 and 2nd in 2001-2014. There was no ranking in 1975 due to unavailable data.