The most detailed assessment so far for how accessibility to the services, institutions and economic opportunities offered by cities varies around the world is published in Nature this week.

Difficulty in accessing urban areas where resources such as health services, education, jobs, banking and financial institutions are concentrated is a major barrier to improved livelihoods and overall development: advancing accessibility worldwide underpins the equity agenda of ‘leaving no one behind’ established by the United Nations’ Sustainable Development Goals (SDGs). The only previous assessment of global accessibility was for the year 2000, but it was conducted before recent expansions in infrastructure networks, particularly within lower-resource settings, and major advances in data quality and availability.

Daniel Weiss and colleagues measure accessibility in terms of travel time required to reach the nearest urban centre, which they define as a contiguous area with 1,500 or more inhabitants per square kilometre or a majority of built-up land cover with a population centre of at least 50,000 inhabitants. They integrate multiple large data sources for road and city geography to create a high-resolution (approximately 1 square kilometre) global map quantifying travel time to cities for 2015. They find that 80% of the global population lives within an hour of a city, but there are disparities in accessibility relative to wealth: only half (50.9%) of people in low income settings (concentrated in sub-Saharan Africa) live within an hour of a city, compared to 90.7% of individuals in high-income settings (concentrated in Europe and North America).

This research provides useful input for future geospatial modelling endeavours, including those that highlight the protective effect of remoteness on wilderness areas, or reinforce the need for strategic road building that avoids unnecessary environmental damage.