NASA's Virtual Earth has many interesting images.

One of them is a composite night time earth lights.

Some interesting observations on this image:

• Look at the Nile as it traverses Egypt. See how dense the population is along its shores.
• The same density is on the southern coast of France, and east coast of Italy, but not to the same continuity on the West coast.
• From Moscow going east, there is a continuum of cities all the way to the Pacific coast, probably facilitated by railroads.
• The old Silk Road is evident from Eastern Iran to the Ferghana Valley going east, with a slight breakage then to China.
• Japan has very high density.
• India and eastern China are both very densely populated (no wonder when they hold 40% of the world population combined).
• What is unusual is the availability of electric power throughout India and Eastern China.
• America's East coast and midwest are very densely populated. The West coast is also that way, but between the midwest and the West coast, there is relatively sparse area.
• The East coast of South America is very dense. The same goes for the northern part. Between them, there is the large Amazon forest.
• In Africa, the highly populated areas are the north West, north East, and South Africa. Apart from a few other single cities (Khartoum), Africa is largely devoid of city lights.
• In the oceans there are many islands that have electricity and lights.
• The Arabian peninsula seems to be more inhabited than one would expect. Even more than the Sahara desert in Africa. The exception is the Empty Quarter (Al-Rub' Al Khali).