Last night I left you with an unusual image of the earth from space, showing not clouds but rather the lights from cities.

More than 100 years after the invention of the electric light, some regions of the globe remain thinly populated and mostly dark, including the interior jungles of Africa and South America and the deserts of Africa, Arabia, Australia, and Asia. Also poorly lit are the northern forests of Canada and Russia, and the great expanse of the Himalayas.

This view shows clearly how cities tend to grow along coastlines and transportation networks. In Russia, many lights are visible along the Trans-Siberian railroad stretching from Moscow through the heart of Asia, while areas around the Nile River really stand out as thicker bright line in northeast Africa. In the U.S., many interstates stand out, connecting the brighter dots of city centers. And finally, on this close-up of our area - it's easy to see the cities along the I-95 corridor as well as many other populated regions.