Reddit mentions of How to Grow More Vegetables, Eighth Edition: (and Fruits, Nuts, Berries, Grains, and Other Crops) Than You Ever Thought Possible on Less Land Than You ... (And Fruits, Nuts, Berries, Grains,)

Rather than slog through the opinions here, I'd pick up Jeavons' "How to Grow More Vegetables (and Fruits, Nuts, Berries, Grains, and Other Crops) Than You Ever Thought Possible on Less Land Than You Can Imagine."

It has comprehensive tables of expected yields for a wide variety of common crops, and specifically highlights those that are space and calorie efficient. You will never spend a better $15.

After various self-experiments on my land and reading up on intensive grow methods (e.g. Jeavons), my back-of-the envelope estimate is 5000 square feet/person. You can get it lower but it's increasingly risky, lacking redundancy for crop failure. That's if people are willing to do some of the work themselves and not wait for monoagriculture to bail them out, because gardening for subsistence is labor intensive. Also assumes a largely vegan diet, without supplementation from hunting/fishing. For a population of 80,000, that works out to about 9200 acres.

To give some back story to the above, I am working an an Ecological documentation project of an island of notable biodiversity nearby where I am (it's a river/riparian ecosystem, and the nearby prairie). Just simply recording what is there with a camera. I will upload the info soon.

This is a concept to further with the paired understanding of the Theory of Island Biogeography, as well as the knowledge of the current push to link up islands of biodiversity across the North American continent, and the consequences of both of these things for human/biosphere survival.

Secondly, I am conducting an experimental study project for this method of agriculture: https://en.m.wikipedia.org/wiki/Biointensive_agriculture [1], http://www.growbiointensive.org/grow_main.html [2],
http://www.amazon.com/How-Grow-More-Vegetables-Eighth/dp/160774189X [3]

^ the above links are an example of a knowledge bridge, which I organize like this: [1] basic intro, [2] more in depth info, [3] practical instruction

This is a useful way to structure a large amount of info within one basic introduction.

I would check out Jeavons thoughts on this. I think he was a pioneer in small scale nutritionally complete farming. I am not sure what the newest edition offers, but the edition I have breaks down nutrients per unit of space per crop.

https://www.amazon.com/How-Grow-More-Vegetables-Eighth/dp/160774189X