Food Sustainability Difficult for Future Cities

I read an article about a project called Grow Calgary, where a group of volunteers from the surrounding area got together to make an urban agricultural farm.  The farm will create produce for the entire city to use and is a community garden where volunteers keep it running.  This type of project is what many of the local inhabitants felt was necessary to keep their city growing.  Future cities, as the article suggests, may end up facing a problem of food sustainability if they are constantly relying on importing food.  If there were to be a drought in the Midwest, or other parts of the world where people are dependent on for food then there would be areas that would be without food.  A community farm enables citizens to be active in their community, as well as create a sustainable food source that they can rely on rather than importing food.  There are places like DC that also have community gardens where citizens pay a group of farmers to farm whatever crop will grow at the time.  The farmers then provide those paying citizens with the food that they have grown.  It enables farmers to have jobs, the community to be active, and to have a sustainable food source.