Street-network Sprawl in Al Dali', Yemen

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.

Al Dali': region in Yemen

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 Al Dali', Yemen on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Al Dali' as of 2014, the overall level of street-network sprawl is 6.14, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 11.74, 8.63, 6.76 and 5.52. In each period, new street development in Al Dali' steadily grows more connected than in the last.

Quantity of street network construction: The street network in Al Dali' spans a total of 979 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 5.52, 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 11.74, 9.36, 7.71 and 6.14. Overall, the SNDi of the aggregate street network has fallen: the street network in Al Dali' has become more connected.

The level of street-network sprawl in new development in Al Dali' fell steadily. To get a sense of how street development has changed in Al Dali', we can consider three of its most populous cities: Qa'atabah, Hammam Damt and Ad Dala. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Qa'atabah followed a zig-zag trend. The level of street-network sprawl in new development in Hammam Damt followed a zig-zag trend. The level of street-network sprawl in new development in Ad Dala followed a zig-zag trend.

How do development practices in Al Dali' fare in comparison to others in Yemen? Most recently in 2001-2014, street construction in Al Dali' was the 4th-most disconnected out of the 16 regions in Yemen. Its position in the ranks since 1975 has fallen; relative to other regions in Yemen, street construction in Al Dali' has become more connected. Al Dali' ranked 1st in 1975, 1st in 1976-1990, 7th in 1991-2000 and 4th in 2001-2014.

As of 2014, the city with the most disconnected street network in Al Dali' is Ad Dala with an SNDi of 4.69, which is highly disconnected. Conversely, the most connected city is Qa'atabah with an SNDi of 3.42, which is highly disconnected. See trends for these cities: Qa'atabah, Ad Dala

The level of street-network sprawl in the aggregate network in Al Dali' fell steadily. To get a sense of how the aggregate street network has changed in Al Dali', we can consider three of its most populous cities: Qa'atabah, Hammam Damt and Ad Dala. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Qa'atabah followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Hammam Damt followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Ad Dala followed a zig-zag trend.

To date, Al Dali' is the 4th-most disconnected out of the 16 regions in Yemen. Its position in the ranks since 1975 has fallen; relative to other regions in Yemen, the street network in Al Dali' has become more connected. Al Dali' ranked 1st in 1975, 1st in 1976-1990, 4th in 1991-2000 and 4th in 2001-2014.