Two layers of government, one address
Most of Miami-Dade is divided into incorporated cities — Miami, Miami Beach, Coral Gables, Hialeah, and dozens more — each running its own government and maintaining its own local streets, sidewalks, and (often) sanitation.
Land that isn't part of any city is "unincorporated Miami-Dade." There, the county government itself is the local authority — county departments do the job a city hall would otherwise do.
A real example: same chain, different city halls
There's a Raising Cane's on Coral Way that gets mistaken for Coral Gables all the time — it's actually in the City of Miami, District 4, represented by City of Miami Commissioner Ralph Rosado. Coral Gables is a separate city entirely, with its own commission and its own mayor, Vince Lago.
Raising Cane's has other locations that make the same point — one in the City of Doral, another in Homestead. Same chain, but each one sits in a different city with its own government and its own elected officials.
And the boundary between two of those cities can be as thin as a single street — cross it, and you've gone from one mayor and commission to a completely different one. Proximity tells you nothing about jurisdiction; the address does.
Why it matters when you report something
A report sent to the wrong government can sit untouched for reasons that have nothing to do with how serious the issue is — that office simply has no authority over that stretch of road or that parcel of land.
A city commissioner can't order a county department to act, and vice versa. Knowing which layer you're in is the fastest way to make sure your report lands somewhere it can actually be acted on.
How to check
Your mailing address's city name is a decent first guess, but it isn't always reliable — plenty of unincorporated addresses carry a "Miami" mailing city out of postal convention, not because the property is inside city limits.
When in doubt, a quick search of the address against Miami-Dade's property or GIS records will tell you definitively whether you're in an incorporated city or unincorporated county land.