densely inhabited district; DID
Official statistical term used in Japanese censuses; often abbreviated as DID. Refers to an area with a population density of 4,000 or more per square kilometer.
In the national census, the population of densely inhabited districts is increasing.
人口集中地区 is the full Japanese statistical term, while ＤＩＤ is the abbreviation used for the same census designation.
Compound of 人口 (population), 集中 (concentration), and 地区 (district). A modern technical term with no historical derivation beyond its components.