外郭

1. Origins, structure, and basic meaning

• Structure: In 外郭 (がいかく), outer 外 and enclosure 郭 combine to denote an outer perimeter.
• Basic usage: 外郭 denotes the outer enclosing part or outline of a city, facility, or shape.

2. Common pitfalls and similar expressions

• Outer boundary and outline
  • It focuses on the boundary structure rather than any area merely far from the center.