How severe was the bombing of Japan during World War II? This map, which translates the damage to cities in the U.S. that had similar population sizes in 1940, gives a better sense of the scale.
The map is the work of Alex Wellerstein, a historian at the American Institute of Physics who explains, "When we talk about the bombing of Japan during the World War II, we usually focus on Hiroshima and Nagasaki. But before the atomic bombs, the United States had already begun a ruinous campaign of bombing Japanese cities with incendiary weapons. Over 40,000 tons of napalm bombs were dropped on Japanese cities before the atomic bombings took place."
Using data from old Air Force maps and population figures from the US Census of 1940, he created the map. You can see the whole thing, which has some interactive features, over at Slate.