I personally think a sustainable city is a city that provides it's citizens with eco-friendly options in power, transportation and food. An eco-friendly city doesn't significantly contribute to the world's carbon emissions. The city would be powered by renewable energy like wind and solar energy. The city would have a transportation network that provides a well developed and convenient transit system. The city would be surrounded by large amounts of farm land that provides organic and locally grown food for the inhabitants.

Jonathan,
This sounds like a great idea. An eco-friendly city needs to make changes to everything, and not just fix one problem. This is like what you were saying before about sustainable options in power, transportation, and food. You also mentioned using solar and wind power. A few years ago, my family installed solar panels on our roof. Almost all, if not the entirety of our house's power comes from them. And if we are on vacation, or use less energy than we produce, it goes back into the power grid. When it goes back into the grid, another house, apartment, business, or school can use it instead! None of it goes to waste. This means that even the solar energy we are not using is being put to work. If more people began to install solar panels on top of their roofs, then we could drastically change the amount of fossil fuels and non renewable resources we need to burn.