Street-network Sprawl in Seattle, United States


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 10262 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.

Seattle: city in Washington, United States

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 Seattle, United States on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Seattle as of 2014, the overall level of street-network sprawl is 4.28, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 3.54, 6.8, 7.0 and 6.47. Street construction in Seattle increased in disconnectivity initially but has since improved. The streets constructed in 1991-2000 were the most disconnected.

Quantity of street network construction: The street network in Seattle spans a total of 16909 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 3.54, 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 3.54, 4.15, 4.24 and 4.28. Overall, the SNDi of the aggregate street network has risen: the street network in Seattle has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.61 points, but between 1991-2000 and 2001-2014, it rose by just 0.04.

Seattle and Washington follow the same trend in the disconnectivity of their street network constructions. The SNDi for both of these peaked in 1991-2000.

How do development practices in Seattle fare in comparison to others in Washington? Most recently in 2001-2014, street construction in Seattle was the 1st-most disconnected out of the 6 cities in Washington. Its position in the ranks since 1975 has risen; relative to other cities in Washington, street construction in Seattle has become more disconnected. Seattle ranked 2nd in 1975, 1st in 1976-1990, 2nd in 1991-2000 and 1st in 2001-2014.

Seattle and United States follow the same trend in the disconnectivity of their street network constructions. The SNDi for both of these peaked in 1991-2000.

How do development practices in Seattle fare in comparison to others in United States? Most recently in 2001-2014, street construction in Seattle was the 70th-most disconnected out of the 315 cities in United States. Its position in the ranks since 1975 has fallen; relative to other cities in United States, street construction in Seattle has become more connected. Seattle ranked 58th in 1975, 22nd in 1976-1990, 63rd in 1991-2000 and 70th in 2001-2014.

Seattle and Washington follow the same trend in the disconnectivity of their aggregate street networks. The SNDi for both of these rose steadily.

To date, Seattle is the 2nd-most disconnected out of the 6 cities in Washington. Its position in the ranks since 1975 has not changed. Seattle ranked 2nd in 1975, 2nd in 1976-1990, 2nd in 1991-2000 and 2nd in 2001-2014.

Seattle and United States follow the same trend in the disconnectivity of their aggregate street networks. The SNDi for both of these rose steadily.

To date, Seattle is the 59th-most disconnected out of the 315 cities in United States. Its position in the ranks since 1975 has fallen; relative to other cities in United States, the street network in Seattle has become more connected. Seattle ranked 58th in 1975, 56th in 1976-1990, 60th in 1991-2000 and 59th in 2001-2014.

As of 2015, Seattle had a built-up area of 1158.29 square kilometers, and a population of 2678205 people.

These are some other cities with approximately the same population: