periphery
fringe *
outer boundary

The outer boundary of this region is called the event horizon.

Where will we draw the outer boundaries of this Europe?

His focus was inner human territory, not outer musical boundaries.

From the outer boundary toward the center the age increased.

At last they reached the outer boundaries of the Empire and found little opposition here.

The six lighted courts are red with the outer boundaries being green.

Also, shape is determined by only the outer boundary of an object.

The fumigators could go at, or even next to, the present outer boundaries of the camp.

The outer boundary of a closed figure usually defines its size.

Depended whether Hubble lived in town, or somewhere else within the outer boundaries.