While I’m sure there are a lot of similar resources that deserve equal mention, I wanted to post a link while it is fresh on my mind. There are a great collection of online maps of Japan available for direct viewing via the website of the University of Texas Perry-Castañeda Library Map Collection. They include a list of US army topographic maps from around 1954 and Japanese city plans from 1945-1946. Wonderful to be able to download this directly and see what these places looked like as of the end of the war.
You might want to also check out their China maps and Chinese historical maps.
If you agree that this is a great resource, consider leaving them a comment thanking them for making it available online via the U of Texas library comment page.