Street-network Sprawl in Raymah, Yemen

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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:

• nodal degree
• dendricity, the tree-likeness of the street network
• circuity, the ratio of the distance by road to the straight-line distance of two locations on the street network
• sinuosity, the curviness of a street

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:

• Global trends toward urban street-network sprawl
• A global assessment of street-network sprawl

To see the state of street-network sprawl across the globe, visit the sprawlmap.

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Raymah: 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 Raymah, Yemen on the sprawlmap

How have Raymah's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Raymah as of 2014, the overall level of street-network sprawl is 9.46, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 7.0, 5.74, 8.98 and 9.36. The disconnectivity of new streets constructed in Raymah fell, then rose. In 1976-1990, new street layouts were the most connected.

Quantity of street network construction: The street network in Raymah spans a total of 881 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 9.36, 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 7.0, 6.36, 9.68 and 9.46. Disconnectivity in Raymah's street network follows a zig-zag trend. In 1976-1990, the region was most disconnected; while it was most connected in 1991-2000.

Raymah in context: Street-network sprawl of new development

The level of street-network sprawl in new development in Raymah was at its lowest in 1976-1990. To get a sense of how street development has changed in Raymah, we can consider one of its most populous cities: Az Zahr. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Az Zahr followed a zig-zag trend.

How do development practices in Raymah fare in comparison to others in Yemen? Most recently in 2001-2014, street construction in Raymah was the 1st-most disconnected out of the 16 regions in Yemen. Its position in the ranks since 1975 has risen; relative to other regions in Yemen, street construction in Raymah has become more disconnected. Raymah ranked 8th in 1975, 4th in 1976-1990, 3rd in 1991-2000 and 1st in 2001-2014.

Raymah in context: Aggregate street-network sprawl

As of 2014, the city with the most disconnected street network in Raymah is Az Zahr with an SNDi of 8.81, which is highly disconnected. Conversely, the most connected city is Az Zahr with an SNDi of 8.81, which is highly disconnected. See trends for these cities: Az Zahr, Az Zahr

The level of street-network sprawl in the aggregate network in Raymah followed a zig-zag trend with an overall increase. To get a sense of how the aggregate street network has changed in Raymah, we can consider one of its most populous cities: Az Zahr. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Az Zahr followed a zig-zag trend.

To date, Raymah is the 1st-most disconnected out of the 16 regions in Yemen. Its position in the ranks since 1975 has risen; relative to other regions in Yemen, the street network in Raymah has become more disconnected. Raymah ranked 8th in 1975, 8th in 1976-1990, 1st in 1991-2000 and 1st in 2001-2014.

Cities in Raymah

• Az Zahr