Street-network Sprawl in Garissa, Kenya

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.

Garissa: region in Kenya

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 Garissa, Kenya on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Garissa as of 2014, the overall level of street-network sprawl is 2.83, 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 2.38, 2.88, 2.55 and 3.19. Disconnectivity in street construction in Garissa follows a zig-zag trend. In 1975, street construction was most disconnected, while construction was most connected in 2001-2014.

Quantity of street network construction: The street network in Garissa spans a total of 2506 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 3.19, which is in the 40th to 60th percentile of disconnectedness.

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 2.38, 2.98, 2.83 and 2.83. Disconnectivity in Garissa's street network follows a zig-zag trend. In 1975, the region was most disconnected; while it was most connected in 1976-1990.

The level of street-network sprawl in new development in Garissa followed a zig-zag trend with an overall increase. To get a sense of how street development has changed in Garissa, we can consider three of its most populous cities: Garissa, Hagadera Refugee Camp and Dadaab. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Garissa rose steadily. The level of street-network sprawl in new development in Hagadera Refugee Camp followed a zig-zag trend. The level of street-network sprawl in new development in Dadaab followed a zig-zag trend.

How do development practices in Garissa fare in comparison to others in Kenya? Most recently in 2001-2014, street construction in Garissa was the 16th-most disconnected out of the 26 regions in Kenya. Its position in the ranks since 1975 has fallen; relative to other regions in Kenya, street construction in Garissa has become more connected. Garissa ranked 12th in 1975, 10th in 1976-1990, 18th in 1991-2000 and 16th in 2001-2014.

As of 2014, the city with the most disconnected street network in Garissa is Garissa with an SNDi of 2.99, which is in the 40th to 60th percentile of disconnectedness. Conversely, the most connected city is Hagadera Refugee Camp with an SNDi of -0.2, which is very well-connected. See trends for these cities: Hagadera Refugee Camp, Garissa

The level of street-network sprawl in the aggregate network in Garissa followed a zig-zag trend with an overall increase. To get a sense of how the aggregate street network has changed in Garissa, we can consider three of its most populous cities: Garissa, Hagadera Refugee Camp and Dadaab. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Garissa rose steadily. The level of street-network sprawl in the aggregate network in Hagadera Refugee Camp followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Dadaab followed a zig-zag trend.

To date, Garissa is the 19th-most disconnected out of the 26 regions in Kenya. Its position in the ranks since 1975 has fallen; relative to other regions in Kenya, the street network in Garissa has become more connected. Garissa ranked 12th in 1975, 7th in 1976-1990, 12th in 1991-2000 and 19th in 2001-2014.