Lights On, Lights Out

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Why We Love It

What if you could distill human movement, ambition, and violence on our planet into one single picture? This story map accomplishes that. We love how it directly compares Earth at Night imagery from 2012 and 2016 to show new or extinguished nighttime illumination. We see an illustration of nighttime light’s dichotomous nature, its ability to reveal progress or tragedy. Notably, the map shows the light from recent electrification in rural northern India and, in contrast, the darkness brought on by cataclysmic civil war in Syria.

Why It Works

Maps with a single binary theme, such as more or less, are understood easily and don’t require legends or other complex explanations. Using the Firefly aesthetic, this map maintains the sense of lights flickering on or off. The effect is actually a derived mathematical result of varying input values arranged in a raster grid. Desaturated imagery allows the data to jump off the screen, captures a sense of nighttime realism, and provides context without the need for many basemap labels.

Important Steps

Georeference the imagery for spatial sentience, allowing for re-projection.

Perform a Minus raster function on the 2012 and 2016 images to derive increased and decreased nighttime brightness.

Create a custom color scheme to brightly paint the pixels representing increased and decreased nighttime brightness, while assigning full transparency to midranges with unchanged nighttime brightness.

Add a dark, desaturated satellite imagery basemap for tone and context. Create a colourised text title that informs on the topic while providing dual service as a legend.

In a Story Map Cascade, walk readers through the data, the phenomenon, interesting examples, and the process.

Requirements

Data

This map uses a series of eight high-resolution nighttime images, in JPEG format, from the Earth at Night Collection by NASA’s Visible Earth team, captured via satellite and processed to show areas of nighttime illumination in 2012 and again, four years later, in 2016.

Analysis

Analysis took a matter of seconds. The Minus raster function quickly compared historic imagery for differences in pixel value. A cursory visual examination proved the results to be fruitful and ready for thematic symbology.

Time

This map was generated rather quickly, perhaps in a matter of two hours altogether. The goal and concept was clear going into the work and the processing was rapid, so tangible results manifested quickly. Most of the time was spent in refining the custom colour scheme used to illustrate increased and decreased brightness.

Second Version

Tips

Consider accessible colours. This map is difficult for readers with colourblindness. A second version was created to overcome this.

Transparent

Tips

Don’t map everything. Pixels for places without change in light appear transparent to reveal only the reference imagery.

Legend

Tips

Instead of a traditional legend, provide information using text blocks, a descriptive title, and a font colour that matches the symbology.

Map Author

John Nelson

John Nelson

@John_M_Nelson | LinkedIn

I have way too much fun looking for ways to understand and visually present data, engage others, and write about it. Otherwise, I’m chasing around toddlers and wrangling chickens. Life is good.

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