Street-network Sprawl in Aichi, Japan

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.

Aichi: region in Japan

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 Aichi, Japan on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Aichi as of 2014, the overall level of street-network sprawl is 0.45, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 0.34, 0.67, 2.19 and 2.34. In each period, new street development in Aichi steadily grows more disconnected than in the last. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.33 points, but between 1991-2000 and 2001-2014, it rose by just 0.14.

Quantity of street network construction: The street network in Aichi spans a total of 50723 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 0.34, 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 0.34, 0.4, 0.43 and 0.45. Overall, the SNDi of the aggregate street network has risen: the street network in Aichi has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.06 points, but between 1991-2000 and 2001-2014, it rose by just 0.02.

The level of street-network sprawl in new development in Aichi rose steadily. To get a sense of how street development has changed in Aichi, we can consider three of its most populous cities: Nagoya, Toyohashi and Gamagori. Out of the three cities, Toyohashi and Gamagori do not follow the same trend as the region. The level of street-network sprawl in new development in Toyohashi peaked in 1991-2000. The level of street-network sprawl in new development in Gamagori followed a zig-zag trend.

How do development practices in Aichi fare in comparison to others in Japan? Most recently in 2001-2014, street construction in Aichi was the 33rd-most disconnected out of the 44 regions in Japan. Its position in the ranks since 1975 has risen; relative to other regions in Japan, street construction in Aichi has become more disconnected. Aichi ranked 44th in 1975, 44th in 1976-1990, 37th in 1991-2000 and 33rd in 2001-2014.

As of 2014, the city with the most disconnected street network in Aichi is Toyohashi with an SNDi of 0.37, which is very well-connected. Conversely, the most connected city is Gamagori with an SNDi of 0.33, which is very well-connected. See trends for these cities: Gamagori, Toyohashi

The level of street-network sprawl in the aggregate network in Aichi rose steadily. To get a sense of how the aggregate street network has changed in Aichi, we can consider three of its most populous cities: Nagoya, Toyohashi and Gamagori. Out of the three cities, Gamagori does not follow the same trend as the region. The level of street-network sprawl in the aggregate network in Gamagori peaked in 1991-2000.

To date, Aichi is the 44th-most disconnected out of the 44 regions in Japan. Its position in the ranks since 1975 has not changed. Aichi ranked 44th in 1975, 44th in 1976-1990, 44th in 1991-2000 and 44th in 2001-2014.