Street-network Sprawl in Yiyang, China

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.

Yiyang: city in Henan, 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 Yiyang, China on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Yiyang as of 2014, the overall level of street-network sprawl is 1.14, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 1.3, 3.68, -0.14 and 1.1. Disconnectivity in street construction in Yiyang follows a zig-zag trend. In 1991-2000, street construction was most disconnected, while construction was most connected in 1976-1990.

Quantity of street network construction: The street network in Yiyang spans a total of 218 kilometers. It is dominated by roads constructed in 1991-2000. These roads have an SNDi of -0.14, 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 1.3, 2.41, 1.13 and 1.14. Disconnectivity in Yiyang's street network follows a zig-zag trend. In 1991-2000, the city was most disconnected; while it was most connected in 1976-1990.

Yiyang and Henan do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Yiyang followed a zig-zag trend with an overall decrease, while the SNDi of street constructions in Henan peaked in 1991-2000.

How do development practices in Yiyang fare in comparison to others in Henan? Most recently in 2001-2014, street construction in Yiyang was the 47th-most disconnected out of the 118 cities in Henan. Its position in the ranks since 1975 has fallen; relative to other cities in Henan, street construction in Yiyang has become more connected. Yiyang ranked 24th in 1975, 3rd in 1976-1990, 76th in 1991-2000 and 47th in 2001-2014.

Yiyang and China follow the same trend in the disconnectivity of their street network constructions. The SNDi for both of these followed a zig-zag trend with an overall decrease.

How do development practices in Yiyang fare in comparison to others in China? Most recently in 2001-2014, street construction in Yiyang was the 973rd-most disconnected out of the 1651 cities in China. Its position in the ranks since 1975 has fallen; relative to other cities in China, street construction in Yiyang has become more connected. Yiyang ranked 725th in 1975, 179th in 1976-1990, 1113th in 1991-2000 and 973rd in 2001-2014.

Yiyang and Henan do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Yiyang followed a zig-zag trend with an overall decrease, while the SNDi of street constructions in Henan peaked in 1976-1990.

To date, Yiyang is the 47th-most disconnected out of the 118 cities in Henan. Its position in the ranks since 1975 has fallen; relative to other cities in Henan, the street network in Yiyang has become more connected. Yiyang ranked 24th in 1975, 7th in 1976-1990, 48th in 1991-2000 and 47th in 2001-2014.

Yiyang and China do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Yiyang followed a zig-zag trend with an overall decrease, while the SNDi of street constructions in China peaked in 1976-1990.

To date, Yiyang is the 1151st-most disconnected out of the 1651 cities in China. Its position in the ranks since 1975 has fallen; relative to other cities in China, the street network in Yiyang has become more connected. Yiyang ranked 725th in 1975, 475th in 1976-1990, 1093rd in 1991-2000 and 1151st in 2001-2014.

As of 2015, Yiyang had a built-up area of 17.82 square kilometers, and a population of 105748 people.

These are some other cities with approximately the same population:

For some related information about population, urban extent and density, and roads, visit the Atlas of Urban Expansion.