I thought I would post the poster specifications for the conference here.
Posters should be formatted as below (or approximate these measurements if printers do not hold A1 paper stock)
841 x 594 mm
33.1 x 23.4in Portrait orientation
Posters will be displayed on vertical boards, secured with thumb tacks or with adhesive putty, so you can bring them to the conference rolled in a tube.
Most people create the posters digitally and have them printed, but, in keeping with the Graphic Medicine ethos, handmade/drawn/painted is OK, too.