Street-network Sprawl in Galle, Sri Lanka

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.

Galle: region in Sri Lanka

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 Galle, Sri Lanka on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Galle as of 2014, the overall level of street-network sprawl is 5.4, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 5.25, 3.45, 6.19 and 6.09. Disconnectivity in street construction in Galle follows a zig-zag trend. In 1976-1990, street construction was most disconnected, while construction was most connected in 1991-2000.

Quantity of street network construction: The street network in Galle spans a total of 3013 kilometers. It is dominated by roads constructed in 2001-2014. These roads have an SNDi of 6.09, 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 5.25, 5.24, 5.29 and 5.4. The SNDi of the aggregate street network in fell at first, but Galle has worsened in disconnectivity since 1990.

The level of street-network sprawl in new development in Galle followed a zig-zag trend with an overall increase. To get a sense of how street development has changed in Galle, we can consider two of its most populous cities: Galle and Ambalangoda. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Galle followed a zig-zag trend with an overall increase. The level of street-network sprawl in new development in Ambalangoda followed a zig-zag trend with an overall increase.

How do development practices in Galle fare in comparison to others in Sri Lanka? Most recently in 2001-2014, street construction in Galle was the 7th-most disconnected out of the 13 regions in Sri Lanka. Its position in the ranks since 1975 has fallen; relative to other regions in Sri Lanka, street construction in Galle has become more connected. Galle ranked 3rd in 1975, 9th in 1976-1990, 6th in 1991-2000 and 7th in 2001-2014.

As of 2014, the city with the most disconnected street network in Galle is Galle with an SNDi of 6.07, which is highly disconnected. Conversely, the most connected city is Ambalangoda with an SNDi of 5.06, which is highly disconnected. See trends for these cities: Ambalangoda, Galle

The level of street-network sprawl in the aggregate network in Galle was at its lowest in 1976-1990. To get a sense of how the aggregate street network has changed in Galle, we can consider two of its most populous cities: Galle and Ambalangoda. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Galle rose steadily. The level of street-network sprawl in the aggregate network in Ambalangoda rose steadily.

To date, Galle is the 7th-most disconnected out of the 13 regions in Sri Lanka. Its position in the ranks since 1975 has fallen; relative to other regions in Sri Lanka, the street network in Galle has become more connected. Galle ranked 3rd in 1975, 5th in 1976-1990, 6th in 1991-2000 and 7th in 2001-2014.