The geographic term “ecumene” is used to describe land that is permanently populated by human society. It can also refer to industrial and agricultural land that is permanently used to sustain the human population.

More than three-quarters of the world’s population lives in the developing world. The term “developing world” is generally used to refer to countries that do not have highly modernized and industrial economies.

Since roughly eight to ten thousand years ago, the population of humanity has climbed consistently, but gradually; however, beginning in the late eighteenth century in England, the Industrial Revolution changed everything. Technological, medical, and economic innovations have greatly increased the number of people that the planet can reasonably support. In the last two hundred years, the population has grown from one billion to over seven billion people.

China, India, Brazil, and Germany each have a larger population than the Netherlands, but they also all have much more land available in which to house that population. Remember, population density is based on the number of people divided by the land size. So a country with a large population and a small land size will have a very high population density. This is true of many European countries, particularly Northern European countries like Belgium, the Netherlands, and Great Britain. You might not have known the different population densities of these five countries, but you need to know that Northern Europe is an especially densely populated part of the world.

Almost all of Western Europe (including France) has a very high population density because a very large number of people live in a relatively small space. The same is true of Japan (which has one of the highest population densities on Earth). Although China and India are both very large countries by land size they are also the two most heavily populated nations on Earth and so are still relatively densely populated. Of these choices only Canada is both extremely large in land-size and relatively unpopulated. Approximately thirty million people live in Canada and it is either the largest or second largest country on Earth (depending on how you measure the polar region). It is one of the least densely populated countries in the world.

For most of human history, the population of Earth has climbed steadily and slowly, but in the eighteenth century (with the beginning of the Agricultural Revolution and the Industrial Revolution in Britain) the population began to grow dramatically. By the first decade of the nineteenth century, the population of Earth was around one billion for the first time in human history. In just over a century, the population would double again to two billion. The population is now in excess of seven billion and still climbing.

Population density refers to the number of people who live in a defined land area (usually square miles or square kilometers). So, if two million people live in ten square miles, the population density is two hundred thousand people per square mile. Population density is usually highest in urban areas, specifically cities like New York City, which keep growing but have a maximum land area. Los Angeles has a similar population level to New York City, but much more room for that population to inhabit. Of course, Los Angeles would still have a much higher population density than, say, the Rocky Mountains or the Alaskan wilderness.

More than half of the world’s seven billion people live in Asia. The next highest continent is Africa, with a little over a billion people. Approximately seven hundred million people live in Europe; four hundred million in South America; five hundred million in North America.

A “primate city” is the largest city in a region. In order to be a “primate city” it must be disproportionately bigger than other cities in the region, primarily because those people who live in the surrounding area migrate to the “primate city” in search of work, education, or entertainment.

Oceania (which includes Australia, New Zealand, and many of the surrounding Pacific Islands) is by far the least heavily populated continent on Earth—excluding, obviously, Antarctica. Oceania has less than fifty million people living there. The next lowest—South America—has a population of four hundred million people.