By Michael A. Verespej Seven of the 10 most expensive cities in the world to live in -- including the Japanese cities of Tokyo and Osaka (the two most expensive cities) -- are in Asia. But the gap between the most expensive and least expensive cities, based on William M. Mercer Inc.'s most recent global cost-of-living survey, has narrowed by 11 index points since September 1998. New York remains the most expensive city in the U.S. (and 13th overall), and the only U.S. city in the top 30. London, at 10th overall, is Europe's most expensive city; Buenos Aires (18th) is the most expensive city in Latin America; and Cairo (17th) is the most expensive city in Africa. Based on the Mercer survey, Tokyo's cost-of-living is nearly 65% higher than New York and 15% higher than any other city in the world.