Street-network Sprawl in Hilmand, Afghanistan

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.

Hilmand: region in Afghanistan

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 Hilmand, Afghanistan on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Hilmand as of 2014, the overall level of street-network sprawl is 2.0, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 7.76, 1.6, nan and 1.11. Data was not available in 1991-2000.

Quantity of street network construction: The street network in Hilmand spans a total of 346 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 1.11, which is relatively well-connected.

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 7.76, 5.26, 5.08 and 2.0. Overall, the SNDi of the aggregate street network has fallen: the street network in Hilmand has become more connected. This decrease has quickened: between 1975 and 1976-1990, SNDi fell by 2.5 points, but between 1991-2000 and 2001-2014, it fell by just 3.07.

The level of street-network sprawl in new development in Hilmand followed a zig-zag trend with an overall decrease. To get a sense of how street development has changed in Hilmand, we can consider three of its most populous cities: Lashkar Gah, Girishk and Sangin. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Lashkar Gah followed a zig-zag trend. The level of street-network sprawl in new development in Girishk followed a zig-zag trend with an overall decrease. The level of street-network sprawl in new development in Sangin followed a zig-zag trend.

How do development practices in Hilmand fare in comparison to others in Afghanistan? Most recently in 2001-2014, street construction in Hilmand was the 22nd-most disconnected out of the 25 regions in Afghanistan. Its position in the ranks since 1975 has fallen; relative to other regions in Afghanistan, street construction in Hilmand has become more connected. Hilmand ranked 6th in 1975, 18th in 1976-1990 and 22nd in 2001-2014. There was no ranking in 1991-2000 due to unavailable data.

As of 2014, the city with the most disconnected street network in Hilmand is Sangin with an SNDi of 3.31, which is highly disconnected. Conversely, the most connected city is Lashkar Gah with an SNDi of 0.51, which is relatively well-connected. See trends for these cities: Lashkar Gah, Sangin

The level of street-network sprawl in the aggregate network in Hilmand fell steadily. To get a sense of how the aggregate street network has changed in Hilmand, we can consider three of its most populous cities: Lashkar Gah, Girishk and Sangin. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Lashkar Gah followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Girishk fell steadily. The level of street-network sprawl in the aggregate network in Sangin followed a zig-zag trend.

To date, Hilmand is the 23rd-most disconnected out of the 25 regions in Afghanistan. Its position in the ranks since 1975 has fallen; relative to other regions in Afghanistan, the street network in Hilmand has become more connected. Hilmand ranked 6th in 1975, 13th in 1976-1990, 14th in 1991-2000 and 23rd in 2001-2014.