The heterogeneity and change in the urban structure of metropolitan areas in the United States, 1990\u20132010

Stefan Leyk,Mark R Montgomery,Hasim Engin,Bryan Jones,Deborah Balk

doi:10.1038/s41597-019-0329-6

Abstract

While the population of the United States has been predominantly urban for nearly 100 years, periodic transformations of the concepts and measures that define urban places and population have taken place, complicating over-time comparisons. We compare and combine data series of officially-designated urban areas, 1990–2010, at the census block-level within Metropolitan Statistical Areas (MSAs) with a satellite-derived consistent series on built-up area from the Global Human Settlement Layer to create urban classes that characterize urban structure and provide estimates of land and population. We find considerable heterogeneity in urban form across MSAs, even among those of similar population size, indicating the inherent difficulties in urban definitions. Over time, we observe slightly declining population densities and increasing land and population in areas captured only by census definitions or low built-up densities, constrained by the geography of place. Nevertheless, deriving urban proxies from satellite-derived built-up areas is promising for future efforts to create spatio-temporally consistent measures for urban land to guide urban demographic change analysis.

Highlights

In 2014, residents of urban areas were estimated to account for 54% of the world’s total population, a figure projected to grow to 66% by mid-century[1]
Using a Global Human Settlement Layer (GHSL) built-up threshold of 50%, we find that of all people living in Metropolitan Statistical Areas (MSAs), from 71.5–74.1% live in urban built-up environments (UAg) depending on census year; some 27.5–25.4% live in officially urban but not built-up (UPO) areas; fewer than 1 percent inhabit Built-up land only (BULO) areas; and from 14.1–10.3% of MSA inhabitants live on rural land (Table 1)
Within MSAs, areas defined as Urban People Only (UPO) comprise more than 62% of urban land in 1990, declining to 55% by 2010

Summary

Introduction

In 2014, residents of urban areas were estimated to account for 54% of the world’s total population, a figure projected to grow to 66% by mid-century[1]. Hidden in such aggregate measures is the great variation across countries in the national definitions of urban, and in the pace and nature of change in such definitions over time[2,3,4]. Definitional changes are in part the result of an evolution in the conceptualization of urban-ness, which has been accompanied by a growing capacity of statistical authorities to distinguish meaningfully between urban land cover and urban population. By accounting for the internal heterogeneity of MSAs, we strive to better understand the complexities of metro areas and their evolution

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Results

Conclusion