Aviation in Indonesia serves as a critical means of connecting the thousands of islands throughout the archipelago. Indonesia is the largest archipelagic country in the world, extending 5,120 kilometres (3,181 mi) from east to west and 1,760 kilometres (1,094 mi) from north to south, comprising 13,466 islands, with 922 of those permanently inhabited. With an estimated population of over 255 million people — making it the world's fourth-most-populous country — and also due to the growth of the middle-class and the advent of low-cost carriers in the recent decade, Indonesia is widely regarded as an emerging market for air travel in the region. Between 2009 and 2014, the number of Indonesian air passengers increased from 27,421,235 to 94,504,086, an increase of over threefold.