In 2006, for the first time in  human history, the number of people living in urban areas equaled the number living in rural areas. This was due to what is often labelled as  the “biggest mass-migration in history”, where the world’s population is moving in masses away from rural areas into urban areas. Naturally, this increase in population will place tremendous amount of pressure on the infrastructures of the world’s cities like public transportation, water supply, power supply, sanitation, solid waste management and others.