All the buildings would be solar powered and wind powered the buildings wouldnt stack up so high. there would be city limits where only bikes and walking was permitted. all fresh fruits and veggies would be grown organically and in the city.

This is a dream, but their are some complications. First off, where could we put all of the solar panels and wind turbines? Also, we would have to find a way to efficiently store energy, better than we can with current tech, as it will not always be a sunny day and a windy night. I personally find that walking and biking works for me in short distances, but not longer ones, like across a large city. Places like Singapore have started building vertical farms that run up skyscrapers. These farms could help grow food within cities.

Adding on to that thought, a sustainable city would need a large stable energy system and enough supplies and resources to spread around. To keep a city healthy and thriving, you would need the technology to have it sustain itself from the inside, such as solar panels or using less gases in machines that release unhealthy fumes. Cities should start to build they own farms and grow crops without wasting the energy of transporting them from far distances. Sustaining a city is hard but if you are able to make a system of energy that conserves the amount of energy a city is using, you could cut back on a lot of waste.