Tomorrow's City - Factfile

People: More than half the world's population already lives in cities, and that number is growing. Each week more than a million people move to urban areas.

Growth: The planet is already home to 23 megacities, meaning cities with more than 10 million people. That number is projected to rise to 36 by 2025.

Water: Securing safe supplies of good quality water for our cities will be one of the greatest challenges of the 21st century. Analysts suggest that on a global level by 2030 we may face a 40% shortfall between forecast demand and available supply of clean water for human and industrial use.

Energy: Applying energy efficiency practices to city buildings can make a very significant impact on greenhouse gas emissions. Eighty per cent of a building's emissions are emitted during its operation phase, and 20 per cent during its construction.

Climate: Buying carbon offsets is one way for businesses to cut their greenhouse gas emissions. One carbon offset represents one metric tonne of carbon dioxide saved from emission into the atmosphere. The carbon is saved by implementing clean energy projects such as hydropower stations, solar parks or wind farms.

Business: Working patterns in our cities are changing as technology allows new forms of connection and communication. The growth in cloud computing is rapid, with the market for cloud professional services worldwide predicted to reach an estimated 5.8 billion euros by 2015. Cloud computing will encourage staff to work from home, and companies to reduce office space, thereby cutting costs.

Innovation: High technology will be one of the hallmarks of tomorrow's city. The cross-pollination of ideas fostered by high-speed communications networks will encourage innovation in many sectors of the economy. Cities are developing R&D hubs that bring together specialists in different disciplines to work on innovative technologies using complimentary skills.

Geography: The balance of power between the world's greatest cities is shifting. It's predicted that by 2025 Shanghai and Beijing will join New York, Tokyo and London in the group of top five cities ranked by GDP. Los Angeles, Paris and Chicago will be squeezed down the rankings.