American Airlines thoughtfully included a 'cloud atlas' in their 1939 system map: http://t.co/FTOM8A6Kxy #routemap
This tweet was posted on November 18, 2014.
United's 1940s colorful US route map also shows the limits of trans-Pacific flight options: http://t.co/awovdf8elK #routemap
This tweet was posted on October 07, 2014.