What an amazing image! It's a composite, done in this manner (copied from the NASA Goddard Flickr page):
This image of North and South America at night is a composite assembled from data acquired by the Suomi NPP satellite in April and October 2012. The new data was mapped over existing Blue Marble imagery of Earth to provide a realistic view of the planet.
The nighttime view was made possible by the new satellite’s “day-night band” of the Visible Infrared Imaging Radiometer Suite. VIIRS detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe dim signals such as city lights, gas flares, auroras, wildfires, and reflected moonlight. In this case, auroras, fires, and other stray light have been removed to emphasize the city lights.
Stunning. Just wonderful. I love the whole world! Boom de yada! (Uh-oh...that song's gonna lodge itself in my head now....)