thinking about cities 8...

The minimum amount of agricultural land necessary for sustainable food security, with a diversified diet similar to those of North America and Western Europe (hence including meat), is 0.5 of a hectare per person. This does not allow for any land degradation such as soil erosion, and it assumes adequate water supplies. Very few populous countries have more than an average of 0.25 of a hectare. It is realistic to suppose that the absolute minimum of arable land to support one person is a mere 0.07 of a hectare–and this assumes a largely vegetarian diet, no land degradation or water shortages, virtually no post-harvest waste, and farmers who know precisely when and how to plant, fertilize, irrigate, etc. [FAO, 1993]

From the FAO (the Food and Agriculture Organization of the United Nations

Other sources indicate the absolute minimum to be 2 acres, including all the resources a family would need including firewood and animal pasture. Other sources state 1.2 acres. 

How many people can live here, on earth? There is a finite number, even if every patch was turned to production, and we lived in tiny tree houses in our cultivated orchards. This number would  not include the wondrous complexity of wildlife and non-human creatures. I do not seek the argument of Malthus. I seek instead to create a new dialog about how we build.

Zoning, itself, is only about a hundred years old. 

Grocery stores, as we know them, are far less than a hundred.

Cars as mass transportation tools are not centenarians. 

Our cities as we are designing them currently are so young.

We still have time to save ourselves from the worst of our imaginary constructions, our collective inability to see beyond what is delivered to us by tax revenue and corporate shells.

Good luck.