I think the big idea for making cities smarter is integration. There exist multiple networks, multiple databases with information from different sources and of different purpose. We can use this information in an integrated way to understand the trends and to check what the situaton is now.
Example: we have information from traffic sensors, bus usage in a certain place. There are construction permits granted in the area (we know how many people will move). We can predict the change to traffic patterns, be able to adjust bus frequency in advance etc.