Towns and cities are growing rapidly, faster than ever before in human history. In 1950, one-third of the world’s people lived in cities. Today, half of the world’s population lives in cities and towns. It is expected that this share will continue to rise to two-thirds, or 6 billion people by 2050.  The scale and pace of this growth is creating unprecedented social, political, cultural and environmental challenges that must be addressed by the global community.