At least one-fourth of the land area of deserts and mountains cannot be inhabited, so this eliminates another 5,000,000 square miles of land surface for human habitation. We are left with approximately 47,000,000 square miles of land surface, at the most, for the world’s human population (Southwick, 1976).
The world now has about 4 billion people, and will probably reach 8 billion within the next 32 years. Theoretically this means, we now have about 85 people for every square miles of inhabitable land surface on the face of the earth, and this will approach 150 people per square miles by the year 2000 A.D. practically, however, the human population is not evenly distributed. In the great urban concentrations of the world, population densities often exceed 50,000 people per square miles.
The amount of living space per person in some cities like Calcutta is less than 20 square feet per person. Further, economic and behavioural needs of man are such that he must cluster together, but in doing so, he creates super densities such as Calcutta, Cairo, London, New York, Paris, Tokyo, Shanghai and Buenos Aires—the slums of which are definitely deleterious to human health and welfare.