Street-network Sprawl in Yemen

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.

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 Yemen on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Yemen as of 2014, the overall level of street-network sprawl is 3.86, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 4.24, 3.12, 4.85 and 3.91. Disconnectivity in street construction in Yemen 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 Yemen spans a total of 37790 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 3.91, 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 4.24, 3.57, 3.83 and 3.86. The SNDi of the aggregate street network in fell at first, but Yemen has worsened in disconnectivity since 1990.

The level of street-network sprawl in new development in Yemen followed a zig-zag trend with an overall decrease. To get a sense of how street development has changed in Yemen, we can consider three of its most populous regions: Amanat Al Asimah, Ibb and Ta`izz. Out of the three regions, Amanat Al Asimah and Ta`izz do not follow the same trend as the country. The level of street-network sprawl in new development in Amanat Al Asimah rose steadily. The level of street-network sprawl in new development in Ta`izz was at its lowest in 1976-1990.

How do development practices in Yemen fare in comparison to others in the world? Most recently in 2001-2014, street construction in Yemen was the 100th-most disconnected out of the 155 countries in the world. Its position in the ranks since 1975 has fallen; relative to other countries in the world, street construction in Yemen has become more connected. Yemen ranked 32nd in 1975, 86th in 1976-1990, 54th in 1991-2000 and 100th in 2001-2014.

The largest city in Yemen is Sana'a, with a population of 2537100 people. Taking into account the entire (i.e. aggregate) street network in Sana'a as of 2014, the overall level of street-network sprawl is 1.33, which is relatively well-connected. The level of street-network sprawl in new development in Sana'a peaked in 1991-2000.

As of 2014, the city with the most disconnected street network in Yemen is Al Mahwit with an SNDi of 8.88, which is highly disconnected. Conversely, the most connected city is Al Jarrahi with an SNDi of -0.11, which is very well-connected. See trends for these cities: Al Jarrahi, Al Mahwit

The level of street-network sprawl in the aggregate network in Yemen was at its lowest in 1976-1990. To get a sense of how the aggregate street network has changed in Yemen, we can consider three of its most populous regions: Amanat Al Asimah, Ibb and Ta`izz. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Amanat Al Asimah rose steadily. The level of street-network sprawl in the aggregate network in Ibb fell steadily. The level of street-network sprawl in the aggregate network in Ta`izz was at its lowest in 1991-2000.

To date, Yemen is the 58th-most disconnected out of the 155 countries in the world. Its position in the ranks since 1975 has fallen; relative to other countries in the world, the street network in Yemen has become more connected. Yemen ranked 32nd in 1975, 56th in 1976-1990, 52nd in 1991-2000 and 58th in 2001-2014.

The largest city in Yemen is Sana'a, with a population of 2537100 people. Taking into account the entire (i.e. aggregate) street network in Sana'a as of 2014, the overall level of street-network sprawl is 1.33, which is relatively well-connected. The level of street-network sprawl in the aggregate network in Sana'a rose steadily.