The United Nations estimates that the world’s population is over 55% urbanized (Link). When you dive deep into the statistics, you find they are messy: countries self report on urbanization,and different countries have different methods for calculating it.
Researchers using high-resolution satellite imagery estimate and a standard algorithm challenge this and instead estimate the world is over 84% urban already.
Out of curiosity, I checked my own district survey, which has the world’s population broken out by provinces and districts. For each province I have the population and area in square kilometers. According to Google, 1 square kilometer = 0.3 square miles, or ~240 acres.
All of the provinces together equate to about 6.9 billion people. (This is not the 2018 population, I know, but the important thing is the relative ratios.)
Provinces with population densities (population / total area) of more than 100 people per square kilometers (or 100 per 250 acres, or 1 per ~2 acres) have a total population of 4.8 billion, or 72% of the world’s population.
Provinces with population densities of more than 1,000 per square kilometer have a total population of 866 million. There are 330 such provinces. These are mostly cities. The most densely populated province in my database, right now, is Macau, with a density of over 57,000 per square kilometer.
Focusing on high-density populations can be a strategic way of penetrating a population, because people will naturally move to more-densely populated places (urbanized areas) for work, etc. And these figures seem to confirm that the world is generally even more urbanized, already, than the “floor” figure of 55%.