Street-network Sprawl in Onitsha, Nigeria

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.

Onitsha: city in Anambra, Nigeria

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 Onitsha, Nigeria on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Onitsha as of 2014, the overall level of street-network sprawl is 3.76, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 2.82, 3.96, 3.49 and 4.05. Disconnectivity in street construction in Onitsha follows a zig-zag trend. In 1975, street construction was most disconnected, while construction was most connected in 2001-2014.

Quantity of street network construction: The street network in Onitsha spans a total of 4605 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 3.96, 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 2.82, 3.75, 3.73 and 3.76. Disconnectivity in Onitsha's street network follows a zig-zag trend. In 1975, the city was most disconnected; while it was most connected in 2001-2014.

Onitsha and Anambra do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Onitsha followed a zig-zag trend with an overall increase, while the SNDi of street constructions in Anambra rose steadily.

How do development practices in Onitsha fare in comparison to others in Anambra? Most recently in 2001-2014, street construction in Onitsha was the 3rd-most disconnected out of the 5 cities in Anambra. Its position in the ranks since 1975 has fallen; relative to other cities in Anambra, street construction in Onitsha has become more connected. Onitsha ranked 2nd in 1975, 1st in 1976-1990, 2nd in 1991-2000 and 3rd in 2001-2014.

Onitsha and Nigeria do not follow the same trend in the disconnectivity of their street network constructions. The SNDi in Onitsha followed a zig-zag trend with an overall increase, while the SNDi of street constructions in Nigeria peaked in 1991-2000.

How do development practices in Onitsha fare in comparison to others in Nigeria? Most recently in 2001-2014, street construction in Onitsha was the 124th-most disconnected out of the 411 cities in Nigeria. Its position in the ranks since 1975 has fallen; relative to other cities in Nigeria, street construction in Onitsha has become more connected. Onitsha ranked 57th in 1975, 58th in 1976-1990, 110th in 1991-2000 and 124th in 2001-2014.

Onitsha and Anambra do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Onitsha followed a zig-zag trend with an overall increase, while the SNDi of street constructions in Anambra rose steadily.

To date, Onitsha is the 2nd-most disconnected out of the 5 cities in Anambra. Its position in the ranks since 1975 has not changed. Onitsha ranked 2nd in 1975, 1st in 1976-1990, 1st in 1991-2000 and 2nd in 2001-2014.

Onitsha and Nigeria do not follow the same trend in the disconnectivity of their aggregate street networks. The SNDi in Onitsha followed a zig-zag trend with an overall increase, while the SNDi of street constructions in Nigeria rose steadily.

To date, Onitsha is the 78th-most disconnected out of the 411 cities in Nigeria. Its position in the ranks since 1975 has fallen; relative to other cities in Nigeria, the street network in Onitsha has become more connected. Onitsha ranked 57th in 1975, 37th in 1976-1990, 51st in 1991-2000 and 78th in 2001-2014.

As of 2015, Onitsha had a built-up area of 261.67 square kilometers, and a population of 3150801 people.

These are some other cities with approximately the same population: