Population Density: wow!

I just did some calculation regarding possible population density for the ‘city’ cylinder. If I give 45 sq meters per person (about 500 sq ft) and use 60%of the surface of the cylinder, i.e. one story dwellings, then the peak population is about 31,000 people. This is a lot more than I expected. It gives a megacity population density with a large town population. I guess now the problem is how much food production is necessary to support that many people?