If the 7,100,000,000 inhabitants of the Earth were evenly distributed across the land area, the population density would be about 125 persons per square mile (48 per square kilometer). However, people are very unevenly distributed, creating huge disparities in density. Mongolia, for example, has 5.2 persons per square mile (2 per square kilometer), whereas Bangladesh has 2897 persons per square mile (1118 per square kilometer) (Figure 3.1).

If we consider the distribution of people by continents, we find that 70.2 percent of the human race lives in Eurasia—Europe and Asia. The continent of North America is home to only 7.7 percent of all people, Africa to 15.2 percent, South America to 5.6 percent, and Australia and the Pacific islands to 0.5 percent. When we consider population distribution by country, we find that 19 percent of all humans reside in China, 17 percent in India, and only 4.4 percent in the third-largest nation in the world, the United States (Table 3.1).

For analyzing data, it is convenient to divide population density into categories. For example, in Figure 3.1, one end of the spectrum contains thickly settled areas having 250 or more persons per square mile (100 or more per square kilometer); on the other end, largely unpopulated areas have fewer than 2 persons per square mile (less than 1 per square kilometer). Moderately settled areas, with 60 to 250 persons per square mile (25 to 100 per square kilometer), and thinly settled areas, inhabited by 2 to 60 persons per square mile (1 to 25 per square kilometer), fall between these two extremes. These categories create formal demographic regions based on the single trait of population density. As Figure 3.1 shows, a fragmented crescent of densely settled areas stretches along the western, southern, and eastern edges of the huge Eurasian continent. Two-thirds of the human race is concentrated in this crescent, which contains three major population clusters: eastern Asia, the Indian subcontinent, and Europe. Outside of Eurasia, only scattered districts are so densely settled. Despite the image of a crowded world, thinly settled regions are much more extensive than thickly settled ones, and they appear on every continent. Thin settlement characterizes the northern sections of Eurasia and North America, the interior of South America, most of Australia, and a desert belt through North Africa and the Arabian Peninsula into the heart of Eurasia.

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There is more we as geographers want to know about population geography than simply population density. For example, what are people’s standards of living and are they related to population density? Some of the most thickly populated areas in the world have the highest standards of living—and even suffer from labor shortages (for example, the major industrial areas of western Europe and Japan). The small principality of Monaco in southern Europe, for instance, is the most densely populated nation in the world; it also ranks among the highest incomes per capita, highest average life expectancies, and lowest unemployment rates. In other cases, thinly settled regions may actually be severely overpopulated relative to their ability to support their populations, a situation usually associated with marginal agricultural lands. Although 1000 persons per square mile (400 per square kilometer) is a “sparse” population for an industrial district, it is “dense” for a rural area. For this reason, carrying capacity—the population beyond which a given environment cannot provide support without becoming significantly damaged—provides a far more meaningful index of overpopulation than density alone. Often, however, it is difficult to determine carrying capacity until the region under study is near or over the limit.

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Sometimes the carrying capacity of one place can be expanded by drawing on the resources of another place. Americans, for example, consume far more food, products, and natural resources than do most other people in the world: 26 percent of the entire world’s petroleum, for instance, is consumed in the United States (Figure 3.2). The carrying capacity of the United States would be exceeded if it did not annex the resources—including the labor—of much of the rest of the world.

A critical feature of population geography is the demographic changes that occur over time. Analyzing these gives us a dynamic perspective from which we can glean insights into cultural changes occurring at local, regional, and global scales. Populations change primarily in two ways: people are born and others die in a particular place, and people move into and out of that place. The latter refers to migration, which we will consider later in this chapter. For now we discuss births and deaths, which can be thought of as additions to and subtractions from a population. They provide what demographers refer to as natural increases and natural decreases.