Fun fact: Zone numbers aren't assigned in sequential order. As the dev blog says:
The first digit tells you which district it’s a part of, and the second digit is the zone’s number within that district. For example, Zone 36 is the sixth zone established in District Three.
The art book map above (dev scribbles aren't shown in the blog!) gives these zones general vibes:
0X - スラム (伍番街等) - Slums (Sector V, etc.)
1X - 庁舎 (Government) - interestingly, it does say ひみつの港... (secret port...) under Zone 10...)
2X - この辺はインフラがあつまってる (Lots of infrastructure)
3X - No general vibes but 36 is labelled as 旧庁舎街 (Old government district?), which I found interesting
4X - 上流階級の住むエリア (Upper-class living area)
The line shown in the image is 300-350 km, but the dev blog says the island is 200-250 km^2.
And yes, I have counted the confirmed zones:
09 (Sector V / "Quarantine Valley"), 10 (Police HQ / "government zone"), 30 (Maison Forest), 32 (Ark Mall), 33 (Harmony Square), 36 (Central City / Rayleigh Plaza), XX (Aegis Research Institute) - places you go to in-game
07 (Union City), 21 (Energy Processing Center), 31 (Artificial Nature Park / National Park), 35 (Central City) - mentioned by name in a police report, in a voice line, or on a sign
08, 23, 26, 27, 28, 29, 34 - mentioned in-game, but no name given
03, 12 - one of Lappy's Ultra Quiz answers, which may not be real