Exploring Global Urbanization Using New Data Chandan Deuskar & Eugenie Birch University of Pennsylvania Presentation at Annual World Bank Conference on Land and Poverty Washington DC, March 22, 2017

Outline Data: ‘urban centers’ from Global Human Settlements Model Strengths and weaknesses of the data set Global picture of urbanization: selected summary statistics

1. The data Global Human Settlements (1990, 2000, 2015) from EC-JRC Built-up areas from satellite imagery (Global Human Settlements Layer) Population data from censuses (CIESIN) distributed to GHSL Standardized urban definition (European Commission ‘degree of urbanization’) Urban Centers (a.k.a. high-density clusters) Pop. Density > 1,500 per sq. km. Pop. > 50,000 Urban Clusters Pop. Density > 300 per sq. km. Pop. > 5,000

Cleaning the data: 13,844 - 4,575 9,269 Original urban centers Removed for being unrealistically small or dense: - 4,575 (493 million people) Disproportionately in South Asia (63% of original Urban Centers removed) and Sub-Saharan Africa (40%) Final list 9,269 (~ 3,330 million people)

2. Strengths and limitations of the data set

Strengths Only urban spatial data set that: Covers the entire surface of the earth Allows measurement of change (1990-2015) Defines urban areas in a consistent manner

Limitations Errors: Built-up layer has errors, but no “ground-truth” for comparison Urban centers removed in cleaning are disproportionately in low and lower-middle income countries Conceptual challenges in measuring change in density: Within a census unit, population is distributed using built-up area, making it impossible to measure the two independently in order to assess their relative change (density) (Only an issue in small urban areas or those with low-res census data) Should the unit of analysis change each year as densities change?

1 sq. km. grid cell with 1500 people, i.e. density of 1500 per sq. km. Cluster boundary 1500 1500 1500 1500 Year 1 1500 1500 1500 1500 1500 1500 There are 36000 people in these cells, all of which are included in the high-density cluster of 24 sq. km. 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500

1 sq. km. grid cell with 1500 people, i.e. density of 1500 per sq. km. Cluster boundary Year 2 The same 36000 people are now spread out over a larger, discontiguous area at a lower density. Keep the same boundary?

Revise the year 2 boundary? 1 sq. km. grid cell with 1500 people, i.e. density of 1500 per sq. km. 1500 500 1500 Cluster boundary Year 2 The same 36000 people are now spread out over a larger, discontiguous area at a lower density. Revise the year 2 boundary?

Retroactively revise the year 1 boundary? 1 sq. km. grid cell with 1500 people, i.e. density of 1500 per sq. km. 1500 1500 1500 Cluster boundary 1500 1500 1500 1500 Year 1 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 1500 Retroactively revise the year 1 boundary?

3. Global picture of urbanization: selected summary statistics

Counts

The greatest number of urban centers are in East and South Asia.

Nearly three-quarters of the world’s urban centers are in middle income countries. Size classification is based on 2015 population.

Nearly 90% of all Urban Centers have populations between 50k and 500k (43% are 50-100k) Size classification is based on 2015 population.

Population

Urban centers in Asia have the greatest number of people Urban centers in Asia have the greatest number of people. Those in Asia and Sub-Saharan Africa are growing fastest.

Urban centers in middle income countries have the greatest number of people, and are growing fastest.

A little under half of the world’s population is in these urban centers as of 2015, with the greatest proportions in MENA and LAC. The relatively flat lines suggest urban growth is happening outside urban centers at the same rate as within.

The proportion of the population in urban centers is twice as high in high income countries as in low income countries.

Small urban centers (smaller than 500k) have the greatest total number of people, with nearly double the population of megacities (10m+). Size classification is based on 2015 population.

In the world as a whole, and in EAP, ECA, South Asia, and Sub-Saharan Africa, populations are becoming more concentrated in the largest urban centers over time. However, populations are becoming less concentrated in the largest centers in the Americas and MENA. Size classification is based on 2015 population.

Populations in all income groups are shifting away from the smallest urban centers. The higher the income group the smaller the proportion of population in small urban centers. Size classification is based on 2015 population.

Density

Urban centers in South Asia are much denser than in the rest of the world. The global average density of urban centers increased slightly.

Lower-middle income countries have the densest urban centers Lower-middle income countries have the densest urban centers. Densities are increasing fastest in low income countries.

Smaller urban centers are losing density slightly while larger ones are becoming denser. In 1990, the smallest urban centers were the densest on average. In 2015, the largest ones were the densest. Size classification is based on 2015 population.

In poorer countries, smaller urban centers are denser than larger ones, but this reverses in wealthier countries.

Conclusion and areas for future research The GHS data set can be extremely useful in understanding global urbanization, but only if it is understood properly. EC is currently: Assessing errors in cluster data Combining population-based and built-up area based urban definitions Future research can: Expand the analysis to include urban clusters Combine these data with other types of data

Thank you cdeuskar@upenn.edu