text: The 23 special wards that make up what is considered Tokyo proper have a population (1997) of 7,830,323 . Tokyo Metropolis extends to the west of the central city and has a population of 11,680,490 (1999). Most of the difference in population is concentrated in the Tama district, which is on the western border of Tokyo. The western reaches of the Tama district and the islands are lightly populated. The population of Tokyo Metropolis peaked in 1987 at about 11,917,000. There has been a decline since then, particularly in the central wards where high land costs and expansion of commercial centers have reduced residential land. Suburban areas in the Tama district and in neighboring prefectures (Kanagawa, Chiba, and Saltarea) have grown rapidly. The Greater Tokyo Metropolitan Area, defined as Tokyo Metropolis plus the urbanized portions of three adjacent prefectures, now totals more than 27 million inhabitants; it is the largest urban area in the world. Crowding is a serious problem, particularly in the 23 wards and close suburbs. In Tokyo Metropolis the population density is 5443 persons per sq km (14,097 per sq mi), while in the 23 wards the density is 13,000 persons per sq km (33,670 per sq mi). By contrast, the average density for Japan as whole, itself a crowded country in comparison to other countries, is 328 persons per sq km (850 per sq mi). Problems that relate to crowding include traffic congestion, high land prices and rents, air and noise pollution, lack of open space and greenery, and blocked access to direct sunlight in areas of high-rise construction.