Street-network Sprawl in South Khorasan, Iran

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.

South Khorasan: region in Iran

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 South Khorasan, Iran on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in South Khorasan as of 2014, the overall level of street-network sprawl is 3.43, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 4.1, 2.54, 2.87 and 3.09. The disconnectivity of new streets constructed in South Khorasan fell, then rose. In 1976-1990, new street layouts were the most connected.

Quantity of street network construction: The street network in South Khorasan spans a total of 3653 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 4.1, 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 4.1, 3.84, 3.78 and 3.43. Overall, the SNDi of the aggregate street network has fallen: the street network in South Khorasan has become more connected. This decrease has quickened: between 1975 and 1976-1990, SNDi fell by 0.26 points, but between 1991-2000 and 2001-2014, it fell by just 0.35.

The level of street-network sprawl in new development in South Khorasan was at its lowest in 1976-1990. To get a sense of how street development has changed in South Khorasan, we can consider two of its most populous cities: Birjand and Qaen. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Birjand peaked in 1991-2000. The level of street-network sprawl in new development in Qaen followed a zig-zag trend with an overall decrease.

How do development practices in South Khorasan fare in comparison to others in Iran? Most recently in 2001-2014, street construction in South Khorasan was the 24th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has fallen; relative to other regions in Iran, street construction in South Khorasan has become more connected. South Khorasan ranked 12th in 1975, 14th in 1976-1990, 21st in 1991-2000 and 24th in 2001-2014.

As of 2014, the city with the most disconnected street network in South Khorasan is Qaen with an SNDi of 2.64, which is in the 40th to 60th percentile of disconnectedness. Conversely, the most connected city is Birjand with an SNDi of 1.86, which is relatively well-connected. See trends for these cities: Birjand, Qaen

The level of street-network sprawl in the aggregate network in South Khorasan fell steadily. To get a sense of how the aggregate street network has changed in South Khorasan, we can consider two of its most populous cities: Birjand and Qaen. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Birjand rose steadily. The level of street-network sprawl in the aggregate network in Qaen peaked in 1976-1990.

To date, South Khorasan is the 13th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has fallen; relative to other regions in Iran, the street network in South Khorasan has become more connected. South Khorasan ranked 12th in 1975, 3rd in 1976-1990, 4th in 1991-2000 and 13th in 2001-2014.