If all the world lived in the lower 48 states of the United States, everyone on earth would have 11,569 square feet of property (assuming there are 7.5 billion of us). That is a piece of property that is 107.5 feet long and 107.5 wide.
Let's say you build a house on this property for yourself that is 30' by 30'. Let's say you also have a solar array that is 30' by 30'. Additionally the roof of the house could be covered in solar panels. 10 meters by 10 meters of solar panels is enough to produce 100 kW of electricity in direct sun. times two if the roof is covered, that is 200 kW during the day and assuming 5 hours of peak performance... that is 100 kWh of electricity (way more than one person could use heating, showering, cooking, and washing clothes). That would take up 1,800 square feet. That leaves 9,769 square feet left to grow food.
What are we spelling out here? This is a formula for overpopulation if all the farm-able land in the world was the size of the contiguous US. In this calculation we will assume that everybody can live off eating algae (yes as if we were all fish).
A 275 gallon water container is 4' by 4' by 4'. In other words it takes up 16 square feet of surface area. Each of these tanks can produce 50 grams of dry algae every 2 weeks in perfect weather.
If a normal person eats a pound of dry food a meal, then it would take 15 of these tanks to feed a person for one day (3 meals). 15 of these tanks would take up 240 square feet of the remaining 9,769 square feet on this piece of property. We would need 14 days of these tanks to allow this to be a non-stop cycle of food growing so a person could eat continuously. 240 square feet, times 14, equals 3,360.
What this means is that there would be enough property left over from feeding one person to grow enough algae, for just under two more people to eat continuously. What this means is that there's enough room on this 107' x 107' piece of property to feed a person perpetually and then enough for that person to export food and turn a profit.
This is not an exercise in isolationist self-sustainable thinking. Rather this is to highlight, it's not that earth is running out of space for all the people in it. It's that we're not using the resources correctly. We don't need to be building walls to protect our resources and way of life. We need to use the resources better (and we need God to show us how to do that).
Now you might argue there's no room for roads and infrastructure. But 11,569 square feet is enough to put in a well and small septic system for one person. If travel is necessary... an electric quadcopter drone should be capable of carrying a person and goods/materials.
