Cities are at the heart of national and global growth . In an increasingly urbanised world , cities are both the source and the solution of many global problems . Not only do urban areas account for over half of the world ’ s population , but they also generate around 80 % of global Gross Domestic Product ( GDP ). Cities , however , are confronted and challenged to become inclusive , safe , sustainable and : smart . And because of its impact , one could say that the battle for sustainability will be lost or won in cities . Cities play a major role in achieving Sustainable Development Goals ( SDGs ). They clearly play a role in SDG 11 – sustainable cities and communities – but cities also impact many other SDGs .