the whole city; citywide
Refers to the entirety of a single city. Often used in news reports about municipal events or policies.
An evacuation advisory was issued for the whole city.
all cities; every city
Refers to multiple cities collectively. Common in contexts like surveys, comparisons, or nationwide policies.
We compared the populations of all the cities.
all citizens; the whole city
Compound of 全 (zen, 'all, whole') and 市 (shi, 'city'). The reading ぜんし follows standard on'yomi.