Extended family groups living under one roof are the most common household type, accounting for 38% of all people. This is followed by two-parent "nuclear" households, with two adults living with their children accounting for 33% of the world’s population. Extended families are also widespread in Asia, including India at 54%. Despite such a large household density, two-parent families are the most common arrangement in the Middle East-North Africa region at 56%. Single parent homes are also widespread, especially in North America and the United Kingdom at 23% and 21% respectively.
The global divergence in household density numbers is partly due to the growing movement away from rural areas towards cities. According to separate figures from the United Nations, 55% of the global population lives in urban areas, a number that is expected to rise to 60% by 2030, and 68% by 2050. Almost 90% of population growth is occurring in Asia and Africa, where incomes are lower, households are larger, and infrastructure is stretched. One in three global citizens currently live in cities with at least 500,000 residents.
There are now 33 megacities in the world, a title given to ultra-large metropolises with more than 10 million inhabitants. By 2030, the world is projected to have 43 megacities, most of them in developing regions. Tokyo is the world’s largest city, with a huge total of 37 million residents. The Japanese megacity is followed by New Delhi with 29 million, Shanghai with 26 million, and Mexico City and São Paulo with 22 million inhabitants. Cairo, Mumbai, Beijing, and Dhaka follow closely behind with 20 million inhabitants. Despite its massive size, numbers are falling in Tokyo, with Delhi projected to become the most populous city in the world by 2028.