Street-network Sprawl in Dayao, China

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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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Dayao: city in Hunan, China

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 Dayao, China on the sprawlmap

How have Dayao's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Dayao as of 2014, the overall level of street-network sprawl is 0.96, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 1.46, 0.34, 1.63 and 1.17. Disconnectivity in street construction in Dayao 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 Dayao spans a total of 106 kilometers. It is dominated by roads constructed in 1991-2000. These roads have an SNDi of 1.63, 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 1.46, 0.48, 0.94 and 0.96. The SNDi of the aggregate street network in fell at first, but Dayao has worsened in disconnectivity since 1990.

Dayao in context: Street-network sprawl of new development

Dayao and Hunan do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Dayao followed a zig-zag trend with an overall decrease, while the SNDi of street constructions in Hunan followed a zig-zag trend with an overall decrease.

How do development practices in Dayao fare in comparison to others in Hunan? Most recently in 2001-2014, street construction in Dayao was the 55th-most disconnected out of the 95 cities in Hunan. Its position in the ranks since 1975 has fallen; relative to other cities in Hunan, street construction in Dayao has become more connected. Dayao ranked 50th in 1975, 81st in 1976-1990, 33rd in 1991-2000 and 55th in 2001-2014.

Dayao and China do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Dayao followed a zig-zag trend with an overall decrease, while the SNDi of street constructions in China followed a zig-zag trend with an overall decrease.

Dayao in context: Aggregate street-network sprawl

Dayao and Hunan do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Dayao was at its lowest in 1976-1990, while the SNDi of street constructions in Hunan peaked in 1976-1990.

To date, Dayao is the 77th-most disconnected out of the 95 cities in Hunan. Its position in the ranks since 1975 has fallen; relative to other cities in Hunan, the street network in Dayao has become more connected. Dayao ranked 50th in 1975, 83rd in 1976-1990, 74th in 1991-2000 and 77th in 2001-2014.

Dayao and China do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Dayao was at its lowest in 1976-1990, while the SNDi of street constructions in China peaked in 1976-1990.

What about other similarly-populated cities?

As of 2015, Dayao had a built-up area of 3.52 square kilometers, and a population of 78506 people.

These are some other cities with approximately the same population:

• Ormoc, Philippines
• Matehuala, Mexico
• Kuwatau, Nigeria