This map shows an unlikely source of America's light pollution

From the bright lights of Times Square to the high-powered flood lights of a suburban Walmart, we expect our cities to give off a certain amount of light pollution. Even though our view of the universe is largely blotted out around city centers, there’s a measure of comfort in knowing an inspiring view of a starry night is only a short drive away.

Increasingly though, economic activity in America’s rural spaces is casting a glow into the sky, and now four out of five people in North America cannot see the Milky Way at night.

Today’s map, from geographer and journalist, Tim Wallace, is a different perspective on light pollution in the United States. The map was created by subtracting population from light output, which highlights areas that throw off more light than predicted given their population density.

On this style of map, it isn’t the glowing metropolitan centers of New York and Los Angeles that stand out, but regions like the oil-rich corner of South Dakota or the final leg of the Mississippi River. Let’s zoom in and investigate what’s happening in these unexpected illumination zones.

Oil & gas

Some of the most prominent patterns on the map appear in regions where shale oil is being extracted.

In a relatively short amount of time, America became the largest oil producer on the planet. One of the major factors that fueled record production for shale oil producers was the proliferation of multi-well pad drilling — when multiple wells are drilled from a single drill site. From the air, it’s easy to spot these well formations spreading across the landscape, but the effect is even more pronounced at night.

At times, oil production is so strong that drillers flare the excess natural gas. In North Dakota alone, there are nearly 14,000 producing wells, and the resulting flares are what create the distinctive grid patterns on the map.

One of the brightest areas per capita in the country is Loving County, Texas. The county has around 100 residents, but more than 6,000 drilled wells.

Industrial activities

Another point of interest on the map is Louisiana’s “petrochemical corridor”, running between New Orleans and Baton Rouge. An overhead view of Southern Louisiana in the daytime will be punctuated by the “ribbon farms” flanking the Mississippi River — a nod to the region’s history of French settlement.

At night though, a different scene emerges. Over 100 sprawling petrochemical facilities run by companies like Dow Chemical and Union Carbide dot the landscape, a patchwork of highly-illuminated plots.

Commercial sprawl

Some types of infrastructure are typically located away from the city center. Airports, power stations, and racetracks, for example, need a lot of space and aren’t the most popular neighbors.

Another type of facility has been replacing farmland in recent years — logistics hubs. Many of the bright spots on the map outside cities show the warehouses and sortation centers that feed our growing demand for e-commerce.

In the example above, companies like Amazon, Home Depot, Dollar Tree, and Ikea have all clustered their facilities in the sparsely populated farmland south of Joliet, Illinois. This trend is repeated around the country, resulting in the “halos” of light that ring most cities on the map.

Flipping the switch on light pollution

Though light isn’t toxic or overtly damaging to the natural landscape, it can still have a serious impact on wildlife, as well as blunting the beauty of the night sky.

The good news is that light is one of the easiest forms of pollution to prevent. New technologies and lighting techniques aren’t just good for our night skies, they’re generally more energy efficient as well.

Just as economic incentive lured buildings and infrastructure to America’s natural spaces, it may be energy efficiency that helps us return more of the night sky to its natural state.