Street-network Sprawl in Gilan, 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.

Gilan: 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 Gilan, Iran on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Gilan as of 2014, the overall level of street-network sprawl is 3.97, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 3.86, 3.77, 5.34 and 4.98. Disconnectivity in street construction in Gilan follows a zig-zag trend. In 1976-1990, street construction was most disconnected, while construction was most connected in 1991-2000.

Quantity of street network construction: The street network in Gilan spans a total of 10360 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 3.77, 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 3.86, 3.84, 3.91 and 3.97. The SNDi of the aggregate street network in fell at first, but Gilan has worsened in disconnectivity since 1990.

The level of street-network sprawl in new development in Gilan followed a zig-zag trend with an overall increase. To get a sense of how street development has changed in Gilan, we can consider three of its most populous cities: Rasht, Bandar-e Anzali and Lahijan. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Rasht peaked in 1991-2000. The level of street-network sprawl in new development in Bandar-e Anzali followed a zig-zag trend with an overall increase. The level of street-network sprawl in new development in Lahijan rose steadily.

How do development practices in Gilan fare in comparison to others in Iran? Most recently in 2001-2014, street construction in Gilan was the 5th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has risen; relative to other regions in Iran, street construction in Gilan has become more disconnected. Gilan ranked 14th in 1975, 2nd in 1976-1990, 2nd in 1991-2000 and 5th in 2001-2014.

As of 2014, the city with the most disconnected street network in Gilan is Bandar-e Anzali with an SNDi of 3.85, which is highly disconnected. Conversely, the most connected city is Talesh with an SNDi of 1.7, which is relatively well-connected. See trends for these cities: Talesh, Bandar-e Anzali

The level of street-network sprawl in the aggregate network in Gilan was at its lowest in 1976-1990. To get a sense of how the aggregate street network has changed in Gilan, we can consider three of its most populous cities: Rasht, Bandar-e Anzali and Lahijan. Out of the three cities, Rasht and Lahijan do not follow the same trend as the region. The level of street-network sprawl in the aggregate network in Rasht peaked in 1991-2000. The level of street-network sprawl in the aggregate network in Lahijan rose steadily.

To date, Gilan is the 5th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has risen; relative to other regions in Iran, the street network in Gilan has become more disconnected. Gilan ranked 14th in 1975, 4th in 1976-1990, 3rd in 1991-2000 and 5th in 2001-2014.