The idea of helping "city dwellers" garden is probably the best idea. But I also know that most of us won't go very far from our homes to actually work in it. Consider having garden centers/green centers/growing centers in various places around the city. We have a large number of parks, and if your use the square foot garden method, it would be easy to create, easy to care for (even for seniors who can't bend and stoop) and it would be very easy to move when it needs to be.
You might also consider using the farthest corners of public schools property. This would give the children attending a particular school, time to learn about planting and growing food. If you want the "green" ideas to continue, we need to teach the next generations how to do it.