Unveiling 25 Years of Planetary Urbanization with Remote Sensing: Perspectives from the Global Human Settlement Layer

Abstract

Abstract:In the last few decades the magnitude and impacts of planetary urban transformations have become increasingly evident to scientists and policymakers. The ability to understand these processes remained limited in terms of territorial scope and comparative capacity for a long time: data availability and harmonization were among the main constraints. Contemporary technological assets, such as remote sensing and machine learning, allow for analyzing global changes in the settlement process with unprecedented detail. The Global Human Settlement Layer (GHSL) project set out to produce detailed datasets to analyze and monitor the spatial footprint of human settlements and their population, which are key indicators for the global policy commitments of the 2030 Development Agenda. In the GHSL, Earth Observation plays a key role in the detection of built-up areas from the Landsat imagery upon which population distribution is modelled. The combination of remote sensing imagery and population modelling allows for generating globally consistent and detailed information about the spatial distribution of built-up areas and population. The GHSL data facilitate a multi-temporal analysis of human settlements with global coverage. The results presented in this article focus on the patterns of development of built-up areas, population and settlements. The article reports about the present status of global urbanization (2015) and its evolution since 1990 by applying to the GHSL the Degree of Urbanisation definition of the European Commission Directorate General for Regional and Urban Policy (DG-Regio) and the Statistical Office of the European Communities (EUROSTAT). The analysis portrays urbanization dynamics at a regional level and per country income classes to show disparities and inequalities. This study analyzes how the 6.1 billion urban dwellers are distributed worldwide. Results show the degree of global urbanization (which reached 85% in 2015), the more than 100 countries in which urbanization has increased between 1990 and 2015, and the tens of countries in which urbanization is today above the global average and where urbanization grows the fastest. The paper sheds light on the key role of urban areas for development, on the patterns of urban development across the regions of the world and on the role of a new generation of data to advance urbanization theory and reporting.

Mapping the Land Cover of Africa at 10 m Resolution from Multi-Source Remote Sensing Data with Google Earth Engine

“…Sentinel-2 and Landsat-8 satellite imagery offer global high and medium resolution multi-spectral data of the Earth's surface, respectively, which characterize different land cover classes based on spectral information [14]. GHSL presents the global spatial representation of human settlement during the past 40 years, which is closely linked with the urban class [46]. NTL data monitors the nighttime world with one of signal sources from city lights, so that it can also be utilized to map urban areas or human settlements [47].…”

Multi-Scale Estimation of Land Use Efficiency (SDG 11.3.1) across 25 Years Using Global Open and Free Data

“…Humans modify land through direct intervention (e.g., agriculture, soil sealing infrastructures, housing, etc.) [5] or by means of the externality of a direct intervention (e.g., pollution) [6], and the synthesis of land use changes often results in biodiversity loss and degradation [7], the depletion of natural resources, and urbanisation, which is a defining trend of the Anthropocene [8][9][10].Contemporary urbanisation processes have attained a planetary reach, as theory [11] and empirical evidence suggest [12], and they are substantially more intense compared to previous epochs [13], with a sizable spatial and demographic connotation. The urbanisation process takes place through spatial expansion and population densification [14][15][16].…”

“…Both layers represent a new generation of EO products that possess high spatial resolution (decametric resolution), abstract artificial land as built-up areas and urban footprints [43,48,49], and have global coverage. Information extracted from these layers provides the most recent representation of the extent of human settlements -2012 in GUF and 2014 [43,50] and substantially contributes to the understanding of the extent of the urbanisation process [12,51]. An additional limitation of several land cover products and urban mapping products is the unavailability or incompatibility of information over time (multi-temporal data) to monitor pattern changes and to identify long-term trajectories of land consumption.…”

“…Contemporary urbanisation processes have attained a planetary reach, as theory [11] and empirical evidence suggest [12], and they are substantially more intense compared to previous epochs [13], with a sizable spatial and demographic connotation. The urbanisation process takes place through spatial expansion and population densification [14][15][16].…”

India’s Emergent Urban Formations

“…1 These national urban policies have become standard practice (in a declaratory sense at least) but they tend to be based on shaky premises of how urbanization unfolds and poor urban data and are in some ways missing out on ground realities. Predictions about future urban growth by the United Nations and other agencies and national governments are equally questionable (Cohen 2004;Satterthwaite 2010;Melchiorri et al 2018).…”