For example, the Organisation for Economic Co-operation and Development (OECD) suggested that most modern mega-cities in countries like Japan, China and France make up over 65% of that country’s total Gross Domestic Product (GDP). The biggest metropolitan areas in the world, ones like Tokyo, Seoul and New York, have populations of over 20 million. This means just these cities have a bigger populations than the Netherlands, Belgium and Greece. Also, cities like New York and Shanghai have bigger economies themselves than most countries do. New York, for example, has a GMP of over $1.33 Trillion.