You've been having some success with your garden plot and have been yearning for backyard chickens like a brooding hen, so you've been wondering: What would it take me to live off my own urban farm? Well, a solar-energy-focused program called One Block Off the Grid has come up with an infographic illustrating how much backyard it would take to feed a family of four. (Thanks to Treehugger for the link.)
Turns out it's not as much space as SFoodie would have suspected. You'd have to make some concessions, of course, to fit it all in: Goats instead of cows. Wheat instead of corn. Even with pigs and chickens, your diet would have to be much lower in meat. Someone would probably need to be on hand to tend the yardfarm, and you'd better hope all your crops succeed and all your chickens lay eggs.
Given all those factors, the organization says, all you need is 2 acres -- perhaps a quarter less if you go vegan or buy your wheat from a grain farm. Sounds doable, eh? In San Francisco, two acres would cost you ... erk.