Street-network Sprawl in Greater Accra, Ghana

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.

Greater Accra: region in Ghana

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 Greater Accra, Ghana on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Greater Accra as of 2014, the overall level of street-network sprawl is 4.09, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 3.47, 3.97, 4.15 and 4.93. In each period, new street development in Greater Accra steadily grows more disconnected than in the last.

Quantity of street network construction: The street network in Greater Accra spans a total of 12614 kilometers. The period with the greatest volume of street construction was 1975. These roads have an SNDi of 3.47, 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 3.47, 3.69, 3.81 and 4.09. Overall, the SNDi of the aggregate street network has risen: the street network in Greater Accra has become more disconnected.

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

How do development practices in Greater Accra fare in comparison to others in Ghana? Most recently in 2001-2014, street construction in Greater Accra was the 6th-most disconnected out of the 10 regions in Ghana. Its position in the ranks since 1975 has risen; relative to other regions in Ghana, street construction in Greater Accra has become more disconnected. Greater Accra ranked 7th in 1975, 7th in 1976-1990, 7th in 1991-2000 and 6th in 2001-2014.

As of 2014, the city with the most disconnected street network in Greater Accra is Somanya with an SNDi of 5.57, which is highly disconnected. Conversely, the most connected city is Accra with an SNDi of 3.86, which is highly disconnected. See trends for these cities: Accra, Somanya

The level of street-network sprawl in the aggregate network in Greater Accra rose steadily. To get a sense of how the aggregate street network has changed in Greater Accra, we can consider two of its most populous cities: Accra and Somanya. Out of the two cities, Somanya does not follow the same trend as the region. The level of street-network sprawl in the aggregate network in Somanya was at its lowest in 1976-1990.

To date, Greater Accra is the 7th-most disconnected out of the 10 regions in Ghana. Its position in the ranks since 1975 has not changed. Greater Accra ranked 7th in 1975, 7th in 1976-1990, 7th in 1991-2000 and 7th in 2001-2014.