層

1. Origins, structure, and basic meaning

• Structure: Written 層 and read そう, it denotes a physical layer or a segment of people sharing a characteristic.
• Basic usage: It appears in colored strata on a cliff face and in the age groups surveyed for opinions.

2. Common pitfalls and similar expressions

• Material layer versus population segment
  • It can be a visible stratum or part of a compound classifying people by age, income, or another trait.