環礁

1. Origins, structure, and basic meaning

• Structure: 環礁 (かんしょう) is an atoll, a ring-like coral-reef landform. It appears as an identified object and a line islands follow.
• Basic usage: A ring-shaped atoll is found on a map; small islands extend along it.

2. Common pitfalls and similar expressions

• Ring landform identified and alignment followed by islands
  • The first を is the whole landform; に沿って makes it an alignment reference. Distinguish an atoll from one merely circular island.