Street-network Sprawl in Southern Finland, Finland

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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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Southern Finland: region in Finland

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 Southern Finland, Finland on the sprawlmap

How have Southern Finland's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Southern Finland as of 2014, the overall level of street-network sprawl is 2.74, which is in the 40th to 60th percentile of disconnectedness.

Trends in street network construction: The SNDis of street construction for the respective time periods are 1.56, 2.55, 3.78 and 4.59. In each period, new street development in Southern Finland steadily grows more disconnected than in the last. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.99 points, but between 1991-2000 and 2001-2014, it rose by just 0.8.

Quantity of street network construction: The street network in Southern Finland spans a total of 17617 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 2.55, which is in the 40th to 60th percentile of disconnectedness.

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 1.56, 2.15, 2.36 and 2.74. Overall, the SNDi of the aggregate street network has risen: the street network in Southern Finland has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.59 points, but between 1991-2000 and 2001-2014, it rose by just 0.38.

Southern Finland in context: Street-network sprawl of new development

The level of street-network sprawl in new development in Southern Finland rose steadily. To get a sense of how street development has changed in Southern Finland, we can consider one of its most populous cities: Helsinki. Disconnectivity in the most populous cities in Southern Finland follow the same region trend.

How do development practices in Southern Finland fare in comparison to others in Finland? Most recently in 2001-2014, street construction in Southern Finland was the 2nd-most disconnected out of the 4 regions in Finland. Its position in the ranks since 1975 has risen; relative to other regions in Finland, street construction in Southern Finland has become more disconnected. Southern Finland ranked 4th in 1975, 4th in 1976-1990, 2nd in 1991-2000 and 2nd in 2001-2014.

Southern Finland in context: Aggregate street-network sprawl

As of 2014, the city with the most disconnected street network in Southern Finland is Helsinki with an SNDi of 0.81, which is relatively well-connected. Conversely, the most connected city is Helsinki with an SNDi of 0.81, which is relatively well-connected. See trends for these cities: Helsinki, Helsinki

The level of street-network sprawl in the aggregate network in Southern Finland rose steadily. To get a sense of how the aggregate street network has changed in Southern Finland, we can consider one of its most populous cities: Helsinki. Disconnectivity in the most populous cities in Southern Finland follow the same region trend.

To date, Southern Finland is the 3rd-most disconnected out of the 4 regions in Finland. Its position in the ranks since 1975 has risen; relative to other regions in Finland, the street network in Southern Finland has become more disconnected. Southern Finland ranked 4th in 1975, 4th in 1976-1990, 4th in 1991-2000 and 3rd in 2001-2014.

Cities in Southern Finland

• Helsinki