Istanbul, as the largest city in Turkey - an important industrial, commercial and cultural center in the region and a shoo-in for being one of the biggest 10 megacities in the world - has a budget bigger than the GDPs of 80 countries including Albania, Macedonia and Armenia.Earlier this week, a record consolidated budget of 31.9 billion Turkish lira ($13.7 billion) was allocated to the Istanbul Metropolitan Municipality for next year, a figure that exceeds the budgets for 19 Turkish ministries.The huge sum begs the question of how fast the city is growing and how to best manage this growth in both population and transportation.According to economists, the budget of 31.9 billion lira - ostensibly an astronomical sum - is really a reasonable amount for the growing population of Istanbul."Istanbul's population, which is officially 15 million, is higher than 130 countries across the world. Unofficially, it has exceeded 17 million people with unregistered inhabitants and domestic and foreign tourists," says Fırat Polat, general coordinator of the Economists Platform, a firm of Turkish consultants.Polat says one of the main drivers behind Istanbul's big budget is its enormous population: "The budget of 31.9 billion Turkish lira seems a sufficient amount to manage this megacity and its population."According to a 2014 United Nations report, the number of megacities - those with more than 10 million people - has increased three-fold globally over the past 24 years.Today there are 28 megacities including Tokyo, Shanghai, Beijing, Sao Paulo, New York, Mexico City, Mumbai, Osaka, Delhi and Dhaka; Istanbul ranks 23rd on the list."For example five years ago, in the beginning of 2010, Istanbul's population was 13 million and the consolidated budget of the municipality was 17.9 billion Turkish lira," says Polat."The number of inhabitants has increased 20 percent in the past five years while the budget has boomed nearly 75 percent. The rise of the budget is more than the rise of population which is totally normal."However, the experts think that dense urban environments may provide certain benefits but generate hazards like transportation problems, traffic jams, pollution and unemployment."This mass rush towards Istanbul has created many problems. With the latest policies, it seems impossible to prevent the population growth of the city," Polat says.The first and maybe the most pressing problem of this growing city is transportation, experts say.