Street-network Sprawl in Varna, Bulgaria

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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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Varna: city in Bulgaria

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 Varna, Bulgaria on the sprawlmap

How have Varna's street networks changed over time?

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Varna as of 2014, the overall level of street-network sprawl is 2.14, which is relatively well-connected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 1.66, 4.94, 9.29 and 6.32. Street construction in Varna 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 Varna spans a total of 697 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 1.66, which is relatively well-connected.

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 1.66, 1.7, 1.8 and 2.14. Overall, the SNDi of the aggregate street network has risen: the street network in Varna has become more disconnected.

Varna in context: Street-network sprawl of new development

Varna and Varna 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 Varna fare in comparison to others in Varna? Most recently in 2001-2014, street construction in Varna was the 1st-most disconnected out of the 1 cities in Varna. Its position in the ranks since 1975 has not changed. Varna ranked 1st in 1975, 1st in 1976-1990, 1st in 1991-2000 and 1st in 2001-2014.

Varna and Bulgaria 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 Varna fare in comparison to others in Bulgaria? Most recently in 2001-2014, street construction in Varna was the 1st-most disconnected out of the 8 cities in Bulgaria. Its position in the ranks since 1975 has risen; relative to other cities in Bulgaria, street construction in Varna has become more disconnected. Varna ranked 4th in 1975, 1st in 1976-1990, 2nd in 1991-2000 and 1st in 2001-2014.

Varna in context: Aggregate street-network sprawl

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

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

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

To date, Varna is the 2nd-most disconnected out of the 8 cities in Bulgaria. Its position in the ranks since 1975 has risen; relative to other cities in Bulgaria, the street network in Varna has become more disconnected. Varna ranked 4th in 1975, 4th in 1976-1990, 4th in 1991-2000 and 2nd in 2001-2014.

What about other similarly-populated cities?

As of 2015, Varna had a built-up area of 37.44 square kilometers, and a population of 283834 people.

These are some other cities with approximately the same population:

• Pangkalpinang, Indonesia
• Hangyulu, China
• Wonosobo, Indonesia