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What is a Densely Inhabited District?
1. Densely Inhabited Districts (DIDs)
(1) Purpose and background
Densely Inhabited Districts are the urban areas that are designated based on statistical data and meet certain criteria, and have been designated in each survey since the 1960 Population Census of Japan against the background described below.
The results of the Population Census of Japan are compiled and used mainly in units of administrative districts, that is, prefectures and municipalities. In particular, cities and wards had been collectively called shi (city) areas, and towns and villages had been collectively called gun (county) areas. Shi areas and gun areas had been generally considered to represent urban areas and rural areas, respectively. However, after the Act for the Promotion of Merger of Towns and Villages and the Act for Promotion of Building New Municipalities were enacted in 1953 and 1956, respectively, many towns and villages were municipalized or merged with the existing cities, and a larger area with the features of rural areas was included in a shi area. As a result, shi areas occupied a significantly larger amount of space than ever, while their population density decreased. Shi areas no longer necessarily represented a feature of urban areas from the aspect of statistics, which imposed an unfavorable influence on statistics.
Therefore, when the 1960 Population Census of Japan was conducted, the Statistics Bureau, Prime Minister's Office (the present Statistics Bureau, Ministry of Internal Affairs and Communications) defined the "Densely Inhabited Districts" in municipalities as a new statistical area unit that showed features of urban areas, whereby data on these Densely Inhabited Districts was incorporated into the results of the Population Census of Japan. Accordingly, it became possible to provide statistical data that help to identify the actual population situation in urban areas, which are used as a standard for calculating distribution of tax revenues to local governments. Besides, they have also been widely used for urban planning, regional development planning, urban redevelopment planning, industrial location planning, transport planning, environmental hygiene measures, crime-and disaster-prevention measures, and various other administrative measures, as well as academic research and private-sector market research.
Densely Inhabited Districts are designated in units of census basic unit blocks, and census enumeration districts if there are several census enumeration districts in a census basic unit block (hereinafter referred to as "basic unit blocks, etc."), and should meet the following criteria, in principle.
1) A district containing basic unit blocks, etc. with a population density of 4,000 or more per square kilometer, such districts being adjacent to each other in a municipality
2) A district consisting of the above adjacent basic unit blocks, etc. whose population is 5,000 or more at the time of the Population Census of Japan
With the idea that Densely Inhabited Districts represent urban areas, a basic unit blocks, etc. which has educational, cultural, and recreational facilities (e.g. schools, laboratories, shrines, temples, athletic fields), industrial facilities (e.g. factories, warehouses, business offices), and communal and social welfare facilities (e.g. public offices, hospitals, sanatoriums), and which is adjacent to the basic unit blocks, etc. mentioned under criteria 1), is also regarded as a district that meets the criteria 1). In this regard, however, population is concentrated in the remaining part excluding the area occupied by those facilities, or those facilities occupy more than half of the area of the whole district.
2. Quasi-Densely Inhabited Districts (Quasi-DIDs)
Some basic unit blocks, etc. with a high population density (basic unit blocks with a population density of 4,000 or more per square kilometer) are adjacent to other such basic unit blocks, etc. in a municipality just like Densely Inhabited Districts, but do not satisfy the criteria for population size. When they are considered to satisfy the criteria, population of 3,000 or more, but less than 5,000, they are designated as a "Quasi-Densely Inhabited District".
Note: A basic unit blocks is a city block or a section divided by permanent facilities, such as roads, rivers, water channels, railways and tracks. Census enumeration districts are designated in units of basic unit blocks.