Street-network Sprawl in Diyala, Iraq

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.

Diyala: region in Iraq

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 Diyala, Iraq on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Diyala as of 2014, the overall level of street-network sprawl is 2.29, which is in the 40th to 60th percentile of disconnectedness.

Trends in street network construction: The SNDis of street construction for the respective time periods are 3.71, 2.07, 2.16 and 2.49. The disconnectivity of new streets constructed in Diyala fell, then rose. In 1976-1990, new street layouts were the most connected.

Quantity of street network construction: The street network in Diyala spans a total of 4961 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 2.07, 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 3.71, 2.15, 2.15 and 2.29. The SNDi of the aggregate street network in fell at first, but Diyala has worsened in disconnectivity since 1990.

The level of street-network sprawl in new development in Diyala was at its lowest in 1976-1990. To get a sense of how street development has changed in Diyala, we can consider three of its most populous cities: Al Khalis, Husainīya and Baqubah. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Al Khalis followed a zig-zag trend with an overall increase. The level of street-network sprawl in new development in Husainīya followed a zig-zag trend. The level of street-network sprawl in new development in Baqubah fell steadily.

How do development practices in Diyala fare in comparison to others in Iraq? Most recently in 2001-2014, street construction in Diyala was the 12th-most disconnected out of the 18 regions in Iraq. Its position in the ranks since 1975 has fallen; relative to other regions in Iraq, street construction in Diyala has become more connected. Diyala ranked 3rd in 1975, 5th in 1976-1990, 11th in 1991-2000 and 12th in 2001-2014.

As of 2014, the city with the most disconnected street network in Diyala is Baqubah with an SNDi of 1.58, which is relatively well-connected. Conversely, the most connected city is Husainīya with an SNDi of 0.98, which is relatively well-connected. See trends for these cities: Husainīya, Baqubah

The level of street-network sprawl in the aggregate network in Diyala was at its lowest in 1976-1990. To get a sense of how the aggregate street network has changed in Diyala, we can consider three of its most populous cities: Al Khalis, Husainīya and Baqubah. Out of the three cities, Husainīya and Baqubah do not follow the same trend as the region. The level of street-network sprawl in the aggregate network in Husainīya followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Baqubah fell steadily.

To date, Diyala is the 7th-most disconnected out of the 18 regions in Iraq. Its position in the ranks since 1975 has fallen; relative to other regions in Iraq, the street network in Diyala has become more connected. Diyala ranked 3rd in 1975, 4th in 1976-1990, 5th in 1991-2000 and 7th in 2001-2014.