Tenured Professor at
The Open University of Japan

Updates Based on Population Changes

　　The nationalized “mdbUA2010 Japan” enabled us to categorize the entire country into 118 urban areas, which provided the basis for our efforts to grasp current conditions in cities.
　　Among several available indices used to examine urban trends, we chose the simplest measure, i.e., population. Generally speaking, cities with upward trends often simultaneously experience a continuous increase in population, with this being vice-versa for those lacking such trends. Although there might be some exceptions to this “rule” for now, this approach is sufficiently tenable to draw up a rough sketch.

3 Patterns of Population Trends

　　The data used to run “mdbUA2010 Japan” – National Version is based on the WGS (World Geodetic System). As of now, data prior to 1990 are available based only on the Tokyo Datum, from which we used four sets of data (in the years 1995, 2000, 2005, and 2010) that were available and comparable with the WGS．
　　Population changes over those four points of time (1995, 2000, 2005, and 2010) were categorized into the following three patterns or trends．
1. Consistent increase
2. Consistent decrease
3. Other(s)
　　Type 1, “consistent increase”, describes an urban area where the population has consistently increased over the four points of time (1995, 2000, 2005, and 2010), whereas type 2, “consistent decrease”, characterizes a city with a consistently decreasing population, and type 3, “others”, includes cases when the population has fluctuated over the four points
　　As a result, we have 52 cities exhibiting a population trend that is categorized as “consistent increase”, 32 cities experiencing a “consistent decrease”, and 34 cities classified under the “others” category. Thus, nearly half the cities are on an upward trend, whereas the remaining centers are either consistently decreasing or fluctuating. It might not be accurate to state that this nation is growing smaller across the board when more than half the cities are not experiencing constant decreases in population. Nevertheless, 1/3 of cities are facing consistent decreases.
　　What needs to be clarified here is the amount of increase/ decrease as well as the way the cities are plotted geographically. For this purpose, the procedure described below was used to categorize cities into several types.

Analysis Procedure and Making of Coefficients

　　After setting the population of the year 2010 as 1.00, the ratio of each population at four points of time during the year 1995-2010 was calculated in percentiles in order to enable ratio-based comparisons of population changes in cities over time. For example, in Hakodate, the actual populations over the four points from 1995-2010 were 179,611; 168,043; 159,350; and 149,482. With the latter value set as 1.0, the resulting ratios are 1.20, 1.12, 1.07, and 1.00, respectively.
　　When the population trend presented a consistent increase such that“1995 < 2000 < 2005 < 2010”, then the city was labeled as Type 1. Conversely, a pattern of “1995 > 2000 > 2005 > 2010” is characteristic of the “consistent decrease” type. Fluctuating or otherwise inconsistent trends were labeled as “other”．
　　After converting them to ratios, the trends for all cities were plotted on a graph, which produced what appeared to be a normal distribution. In order to further categorize cities based on degrees of population change, averages and standard deviations were calculated using the differences between the largest and the smallest ratio values for each city, and Z-scores for each city were calculated using the resulting values. Z-scores are positively correlated with change, such that negative scores represent smaller degrees of change whereas positive scores denote more significant changes. Thus, it was possible to compare population changes for individual cities with national averages over time.
　　The above-described procedure resulted in the classification of five categories of population trends: (1) consistent increase with greater change; (2) consistent increase with smaller change; (3) consistent decrease with greater change; (4) consistent decrease with smaller change; (4) other. The map in the section below illustrates cities according to these five categories.