The USA Today build its own sprawl index and reports on how different metropolitan areas score on it. According to the index, Nashville is the nation's most sprawling metropolitan area of 1 million residents or more with a score of 478. New York scores only 82, and Los Angeles scores a 78. The index is based on analysis of census data. A major finding is that a boom in population does not necessarily trigger sprawl, and that it occur when the population in a metropolitan area is shrinking. Another finding is that availability of water, geography, government and culture are the most important factors in limiting or allowing sprawl. For example, "L.A.'s expansion is narrowed by the ocean, mountains and limited water," the story reports.