Meaning and local context
In Atlanta, “the Perimeter” means Interstate 285 around Atlanta. A central local geography and traffic reference.
Example in context
A local example is “Traffic is bad on the Perimeter.” In plain English, that means “Traffic is bad on Interstate 285.”
Traffic is bad on the Perimeter.
Traffic is bad on Interstate 285.
How to interpret it
The surrounding sentence is important when interpreting “the Perimeter”. Use the regional sense above when the situation matches the example instead of relying on the word or phrase in isolation.
Tone and caution
Do not confuse it with a generic boundary. Because this is informal regional language, tone and situation should guide whether you use “the Perimeter” yourself or simply recognise it when someone else uses it.