An ideal sustainable city would probably be one that has low carbon and other greenhouse gas emissions, not a lot of factories which leads to reduced pollution, and not a lot of cars since cars contribute to pollution as well. A sustainable city should also have recycling areas, and the selling of environmentally friendly products in stores. A sustainable city should have public transportation as well. Sustainable cities are important because they reduce the amount of greenhouse gases being sent into the atmosphere, and thus reducing things like climate change. Sustainable cities also reduce the carbon footprint of a city.

I agree wholeheartedly! Establishing a system of public transportation that's actually good is really important. Europe has done such a good job of it already. If other leading world countries modeled themselves after that and/or built upon what they already have, public transportation would be amazing! And not only public transportation, but also cities of green, too. Green roofs, green walls, plants and trees in every conceivable location! It would do an amazing job of keeping the cities cooler and the air cleaner. And not only those things either! There is so much more humans can do to make our cities more sustainable!