Street-network Sprawl in Lanzhou, 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.

Lanzhou: city in Gansu, 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 Lanzhou, China on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Lanzhou as of 2014, the overall level of street-network sprawl is 4.4, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 4.37, 4.94, 4.2 and 4.73. Disconnectivity in street construction in Lanzhou 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 Lanzhou spans a total of 1674 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 4.37, 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 4.37, 4.4, 4.4 and 4.4. Overall, the SNDi of the aggregate street network has risen: the street network in Lanzhou has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.03 points, but between 1991-2000 and 2001-2014, it rose by just 0.0.

Lanzhou and Gansu do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Lanzhou followed a zig-zag trend with an overall increase, while the SNDi of street constructions in Gansu was at its lowest in 1991-2000.

How do development practices in Lanzhou fare in comparison to others in Gansu? Most recently in 2001-2014, street construction in Lanzhou was the 4th-most disconnected out of the 34 cities in Gansu. Its position in the ranks since 1975 has fallen; relative to other cities in Gansu, street construction in Lanzhou has become more connected. Lanzhou ranked 3rd in 1975, 5th in 1976-1990, 2nd in 1991-2000 and 4th in 2001-2014.

Lanzhou 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 increase.

How do development practices in Lanzhou fare in comparison to others in China? Most recently in 2001-2014, street construction in Lanzhou was the 121st-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 Lanzhou has become more connected. Lanzhou ranked 85th in 1975, 63rd in 1976-1990, 104th in 1991-2000 and 121st in 2001-2014.

Lanzhou and Gansu do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Lanzhou rose steadily, while the SNDi of street constructions in Gansu fell steadily.

To date, Lanzhou is the 5th-most disconnected out of the 34 cities in Gansu. Its position in the ranks since 1975 has fallen; relative to other cities in Gansu, the street network in Lanzhou has become more connected. Lanzhou ranked 3rd in 1975, 6th in 1976-1990, 5th in 1991-2000 and 5th in 2001-2014.

Lanzhou and China do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Lanzhou rose steadily, while the SNDi of street constructions in China peaked in 1976-1990.

To date, Lanzhou is the 70th-most disconnected out of the 1651 cities in China. Its position in the ranks since 1975 has risen; relative to other cities in China, the street network in Lanzhou has become more disconnected. Lanzhou ranked 85th in 1975, 68th in 1976-1990, 64th in 1991-2000 and 70th in 2001-2014.

As of 2015, Lanzhou had a built-up area of 146.6 square kilometers, and a population of 2365069 people.

These are some other cities with approximately the same population: