Street-network Sprawl in Sulu, Philippines

---

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.

---

Sulu: region in Philippines

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 Sulu, Philippines on the sprawlmap

How have Sulu's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Sulu as of 2014, the overall level of street-network sprawl is 3.95, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 3.94, 3.83, 3.05 and 6.33. The disconnectivity of new streets constructed in Sulu fell, then rose. In 1991-2000, new street layouts were the most connected.

Quantity of street network construction: The street network in Sulu spans a total of 988 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 3.83, 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 3.94, 3.85, 3.59 and 3.95. The SNDi of the aggregate street network in fell at first, but Sulu has worsened in disconnectivity since 2000.

Sulu in context: Street-network sprawl of new development

The level of street-network sprawl in new development in Sulu was at its lowest in 1991-2000. To get a sense of how street development has changed in Sulu, we can consider one of its most populous cities: Jolo. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Jolo rose steadily.

How do development practices in Sulu fare in comparison to others in Philippines? Most recently in 2001-2014, street construction in Sulu was the 14th-most disconnected out of the 51 regions in Philippines. Its position in the ranks since 1975 has risen; relative to other regions in Philippines, street construction in Sulu has become more disconnected. Sulu ranked 19th in 1975, 40th in 1976-1990, 49th in 1991-2000 and 14th in 2001-2014.

Sulu in context: Aggregate street-network sprawl

As of 2014, the city with the most disconnected street network in Sulu is Jolo with an SNDi of 2.67, which is in the 40th to 60th percentile of disconnectedness. Conversely, the most connected city is Jolo with an SNDi of 2.67, which is in the 40th to 60th percentile of disconnectedness. See trends for these cities: Jolo, Jolo

The level of street-network sprawl in the aggregate network in Sulu was at its lowest in 1991-2000. To get a sense of how the aggregate street network has changed in Sulu, we can consider one of its most populous cities: Jolo. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in the aggregate network in Jolo rose steadily.

To date, Sulu is the 41st-most disconnected out of the 51 regions in Philippines. Its position in the ranks since 1975 has fallen; relative to other regions in Philippines, the street network in Sulu has become more connected. Sulu ranked 19th in 1975, 35th in 1976-1990, 44th in 1991-2000 and 41st in 2001-2014.

Cities in Sulu

• Jolo