A big thanks to Quizzer6794 for teaching me how to avoid horizontal gaps between pieces, eg see his US State Picture Puzzle Game #3... does anyone know how to remove vertical lines too?!
Looks like the world map is behind bars! Turns out you can't actually remove the vertical lines... if you notice when you guess an answer correct with these pieces, there is an extra gap to the east of each picture. :( Anyway thank you for the hyperlink and the link to my third picture puzzle!