You can see on the map on page 218 in the core rulebook an example map and on that you can see that 1 square equals 1 zone. You can see the same on the Black Ziggurat map on page 273.
Right, but do those correspond to combat zones? E.g., area 4 on the map on p. 273 is 1 zone large. Does that mean a combat that occures in Area 4 would only be 1 zone in size, or are combat zones different?
p. 39 says "How big a zone [in combat] is varies – from a few steps across up to about 25 meters." In combat, a PC can move 1-2 zones in the space of 5-10 seconds. In a delve, it takes 15 minutes (a stretch) to move 1 delve map zone, i.e, one
marker. This makes me think they are different, but the game is unfortunately using the same terminology for both.