blue-line district; area of illegal prostitution
Historical term for areas where illegal prostitution occurred, marked by a blue line on police maps from the 1940s until 1956, when the Anti-Prostitution Law was enacted.
In postwar Tokyo, there were several areas known as blue-line districts.
青線地帯は、警察の地図で青い線で囲まれていたことからその名がついた。
The name 'blue-line district' came from the fact that these areas were enclosed by a blue line on police maps.