Looking at Earth at night from space turns the planet’s extremely varied and complex surface into a much simpler view of light and dark. The ghostly outlines of continents, laced with webs of light, are beautiful and eerily peaceful. But these images can also reveal clues about what the humans on Earth are up to, and how that is changing.
Earlier this year, NASA released a new global mosaic of Earth’s night-lights based on images collected throughout 2016. Cartographer John Nelson was intrigued by the comparison with the 2012 mosaic. NASA’s image sliders, which show a spot of Earth from both of those time periods, revealed changes in the quantity or brightness of lights. Nelson decided to map those changes.
Nelson, a cartographer at the mapping-software company Esri, compared the equivalent pixels on two different maps and calculated the difference by subtracting the brightness value of one from the other. He then mapped those differences, showing places where the 2016 mosaic was brighter in blue, and places that had dimmed in pink. These images reveal clues about what the humans on Earth are up to, and how things are changing.