Themed sets are usually 16x20 or 18x24 in total size, with a varying number of different images.
Most doors and other themes feature 16 photos, but Irish Doors has 32 (one for each county) and Italian Doorways has 20 (one for each region). Camino Doorways also has 32, Doorways of the World has 49, and the epic 32x40 100 Pint-Sized Pubs has, you guessed it, 100.

These take longer to make since the mats have multiple openings cut to display individual little photographs that are printed and then trimmed and mounted by hand.

NOTE: Some photos below do not show the entire mat. The top, side, and bottom borders are larger than pictured. Also, all mats are white and the same, even though they may look different in these images. Some of these sample images were shot in poor conditions, but the actual real photos and mats will of course look much better.