I live in the country and have a big garden.  I understand there is a big push in cities for urban agriculture though.
In urban areas, people need more access to fresh produce
Where do they put gardens?  In the city park?
These agricultural areas can be integrated into local town planning.  But I have heard of roof gardens.
Roof gardens?  Tell me how they manage that.  I would think the dirt would be too heavy and put too much strain on the roof.
Peri-urban  agriculture may have different characteristics. For example, you might not use real soil.
Really?  I have heard of hydro-plants.  Do they use water instead?
Urban agriculture can use aquaculture.  Other things may be as exotic as bee keeping
I've always been fascinated with people who are bee keepers.  I'd be afraid, but they seem to know how to handle bees gently.
Unfortunately, bees have been undergoing colony collapse disorder where the workers bees leave the colony