prefecture-by-prefecture map; atlas of Japan by prefecture; map of a single prefecture
Refers to a map or atlas organized by prefecture, or a map showing a single prefecture. The exact meaning depends on context.
この分県地図は各県の主要都市がよくわかる。
This prefecture-by-prefecture map clearly shows the major cities of each prefecture.
旅行の計画を立てるために、分県地図を買った。
I bought a map of a single prefecture to plan my trip.