The German city of Hamburg has announced an ambitious plan to create, and link, an amazing 27 square miles of new and existing green space all over the city. The plan, called the "Green Network," will effectively remove all cars from the city centre and promote cycling and public transport - and it is planned to be in place by 2034.

If fully realised, the network will cover some 7000 hectares, over half the size of Boston or San Francisco.