Fun fact: The Segoe typeface that Microsoft uses extensively was named after Segoe Road in Madison, WI. I mention it because it's a good example: The street is a boulevard almost 2.5 miles from end-to-end, with an enormously-wide right-of-way. If we were to take just the median strip, about 20 feet wide, that's about 6 acres of land, or enough to feed 12 people for a year. If we took half of the ROW, that's 18 acres of land, or enough to feed 36 people. And if we took 2/3rds, leaving a very adequate 40-foot-wide street, that's 60 people fed.

And that's just one boulevard in a whole city. There are plenty more wide streets that don't need to be. Add in land from parking lots. Repeal the grass lawn ordinance and let people grow food in their front yards. Grow food on commercial building roofs, as some grocery stores have started to do. Wisconsin also has a successful hydroponic grow operation, Superior Fresh, that produces a lot of food in a relatively small footprint, and provides fresh, local produce even in January, so that's a possibility. Add all of that up, there's plenty of land in the city, not even counting the handful of farms that still exist within city limits.