Socialist cities make the same demands on rural areas that capitalist cities do. It's primarily a function of population density, not economic model.

At best, a square mile of farmland can feed about 6000 people. That's under ideal conditions and assuming vegetarians. Want a little meat in your diet, and 2500 is a more realistic number.

A square mile of Chicago contains about 12,000 people. That's 2 to 4.8 square miles of farmland for every square mile of city. Chicago is about 230 square miles.

A square mile of New York contains about 30,000 people. That's 5 to 12 sq miles of farmland for every square mile of city. New York is about 300 square miles.

A square mile of Paris contains about 53,000 people. 8.8 to 21.2 sq miles of farmland for every square mile of city. Paris is about 40 square miles.