According to 1960 U.S. Census, this Region, defined by Regional Plan Association, had about 16.1 millions. The population of 1850 was only one twelfth of 1960's, and New York Metropolitan Region of that time is considered to have been in the sphere of 7-8 miles from City Hall at most; smaller than the present Core part.By 1900, it had the increase of 4.2 millions for the fifty years, and it filled up almost the 20 mile ring with the density of more than 200 persons per square mile. Especially, the growth of Manhattan, Brooklyn and Hudson counties in the Core was tremendous. The most noticiable characteristic of the distribution pattern of 1900 is the leap-frog and linear growth pattern beyond the 20 mile ring. It means that the suburban railroad's early influence on the distribution of population or suburbanization was coming out at the turn of century.From 1900 to 1930, this region gained the increase of 6.1 millions, and, especially, in the last decade, it had the greatest increase on its history. In spite of it, CBDs of the Core, ranging from Manhattan to Newark, began to decrease in population density in that time. And the increasing population filled up mainly the 20 mile ring in New Jersey side and 30 mile ring in Westchester and Long Island. Beyond that, the radial and leap-frog pattern became more predominant than 1900's.It shows the influence of the best age of the suburban railroad in this Region. But, generally speaking, the spacial expansion of 1930 was not so different from 1900's, except Long Island's extraordinary growth.By 1960, this Region had the net gain of 4.5 millions; smaller than the first 30 years' increase. In spite of it, its spacial expansion is much larger than 1930's. The 40 mile ring has been almost filled up with the density of over than 200p.s.m. and the radial growing pattern of the pre-war time is going to be extinguished and to make a round pattern as a whole. The 20 mile ring has been pluged up with the density of over than 5000p.s.m., and the 30 mile ring with over than 1000p.s.m.Long Island Sector and Bergen county are most outstanding in the development.On the other hand, the decrease of the Core has reached the climax; 583 persons per square mile in average from 1950 to 1960. Especially, Manhattan had the decrease of 260, 000 persons and 11, 688 per square mile after 1950. Really, it may be called the population explosion of New York Metropolis.The suburbanization of the pre-war time was the cohesion type around a passenger station and the post-war one is the scattering type around a station. It is different from the suburban sprawl of the western cities in the United States.The distance of 20 miles from Manhattan CBD has always had a meaningful influence to the suburbanization through the pre and post war time. The concentration of population in the 20 mile ring has always been most vigorous, and it coincides with the multi-family dewelling and, beyond that, it shifts to the area scattering suburbanization.