19.20.21. is a research website on "19 cities in the world with 20 million people in the 21st century." With most of the world's population now living in cities, these great urban hubs are key to understanding and shaping global social, political and ecological developments. Or as the site's mission claims, "the rise of the supercities is the defining megatrend of the 21st century."
One example is that most of these supercities border on the oceans of the world, and are thus threatened early on by rising sea levels caused by climate change. The Dutch Randstad, though not nearly large enough to make it to the 19.20.21 list, falls into this category as well.
Very effectively designed in Flash, the site boasts an ambitious five-year plan with research findings in five different media - but unfortunately lacks any information on who's behind the project.