Street-network Sprawl in Changning, 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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Changning: 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 Changning, China on the sprawlmap

How have Changning's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Changning as of 2014, the overall level of street-network sprawl is 0.23, which is very well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 0.08, -0.09, nan and 0.38. Data was not available in 1991-2000.

Quantity of street network construction: The street network in Changning spans a total of 64 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of -0.09, which is very 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 0.08, -0.08, 0.13 and 0.23. The SNDi of the aggregate street network in fell at first, but Changning has worsened in disconnectivity since 1990.

Changning in context: Street-network sprawl of new development

Changning and Hunan do not follow the same trend in the disconnectivity of their street network constructions. There was not enough data from the city, while the SNDi of street constructions in Hunan followed a zig-zag trend with an overall decrease.

How do development practices in Changning fare in comparison to others in Hunan? Most recently in 2001-2014, street construction in Changning was the 70th-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 Changning has become more connected. Changning ranked 71st in 1975, 84th in 1976-1990 and 70th in 2001-2014. There was no ranking in 1991-2000 due to unavailable data.

Changning and China do not follow the same trend in the disconnectivity of their street network constructions. There was not enough data from the city, while the SNDi of street constructions in China followed a zig-zag trend with an overall decrease.

Changning in context: Aggregate street-network sprawl

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

To date, Changning is the 93rd-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 Changning has become more connected. Changning ranked 71st in 1975, 88th in 1976-1990, 89th in 1991-2000 and 93rd in 2001-2014.

Changning and China do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Changning 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, Changning had a built-up area of 8.12 square kilometers, and a population of 138156 people.

These are some other cities with approximately the same population:

• Ksar Hellal, Tunisia
• Talegaon, India
• Barnala, India