Published in 1944, mapmaker Sally De Long's "Our New Neighbors" beautifully depicts projected air routes of the mid-20th century. The dawn of the Air Age, the 1940s were when many airlines first began making international flights.
Via Old Map Gallery, whose curators call attention to feature of the map that you may have missed (emphasized below):
A stunning decorative next step for air age maps. Drawing from the foundational approach of Richard Edes Harrison of showing the world from an "Air Age" perspective, this colorful and deco influenced work gives a simple and elegant view of the world, as set amongst the planets. Centered on the North Pole and showing all the major cities from continent to continent, it includes vignettes for fish and animals throughout, and is highlighted throughout with silver metallic ink.
A far cry from the mind-boggling weave of intercontinental traffic we see today, is it not?
It wasn't initially clear to me how many of these routes were established at the time of the map's printing. The use of the word "projected" in the map's small print at first struck me as ambiguous; projected can obviously mean "planned," "expected," or "forecasted," but it can also mean, in cartographical applications, to map something on a plane surface (the further specification that these routes depict "great circle mileage," i.e. the shortest distance between two points along the curved surface of a sphere, added to my confusion). Upon further consideration, however, the former seems more likely – especially since the map's small print also indicates it was prepared by Western Air Lines, which, judging from the airlines' history, probably didn't have this many international air routes up and running. Still, I wonder how many of these routes were in use by other airlines by the middle of the 20th century.
Via Old Map Gallery, where an original print can be yours for a cool $430.