Interesting. And it affects other countries too.

In Australia, all maps used to enter public domain 50 years after publication.... until the US-Australia free trade agreement of 2005, when non-government mapping copyright was extended to 70 years.

So here, all maps pre-1955 are public domain, and government mapping (from any government, worldwide) up to 1967 is public domain. 

Government mapping dated 1968 will enter public domain on 1 January 2019, per the 50-year rule.

But non-government mapping continues to suffer the 20-year hiatus too: private commercial maps from 1956 won't enter the public domain until  1 Jan 2026... all because of Mickey Mouse and Sonny Bono. 

As for book, the protection is life+70, so authors dying in 1948 will have their entire published oeuvre become public domain on 1 Jan 2019. Looks like we have 25 years on you there!

Brendan Whyte

National Library of Australia