subarea

sub- +‎ area

subarea (plural subareas)

1. A physical region that makes up part of an area.
2. Part of a topic or discipline.
   • 2021, Paul C. van Oorschot, Computer Security and the Internet, page xxv:

     Books like this aim to arrive at a more unified understanding of a broad area, and how its subareas are related.

• subareal

• abasure