I never tire of satellite images, and especially those of North Korea at night. Take a look at the latest image by astronauts aboard the International Space Station. South Korea and China are readily visible - their cities and industries lighting up the night sky. But in between.... is that an ocean?
Not an ocean in the literal sense, but perhaps in terms of an open expanse of... nothingness. Except we know millions of people live and work in North Korea. During the day a satellite image would reveal roads and cities and settlements. But at night? Darkness.
Props to: Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth."