A believe that the typical equirectangular projection is 2:1. Equirectangular is also convenient for turning into an orthographic projection, so I like it despite its distortions. The map I am doing is built as 36x18, with a 6 inch space at the bottom for whatever I want to put there. This takes the map to 36x24 which is a good poster size. I am a few days from being ready for the first test print on poster sized format.