The population density of the United States is closest to 35 persons per square kilometer. To arrive at this answer choice, divide the population of the US (320 million people) by the geographic land area of the US (9 million kilometers).

320 million people /9 million square km = 35.56 or approximately 35 persons per square km.

In 2014, Indonesia had the largest Muslim population in the world. With more than 200,000 Muslims residing there, Indonesia was home to more than twelve percent of the world's Muslim population at the time.

In 2013, Mexico was the birthplace of the largest share of the United States of America's foreign born immigrant population, accounting for almost one-fourth of America's total foreign-born population.

This population pyramid would portrays the population of a college town. The large population within the 20 to 30 population group shows the presence of a university. A retirement community would have almost no one under the age of 55. Populations with high birth rates have pyramids with large bases, while populations with low birth rates are shaped like rectangles.

College towns have a higher population of males and females around the age of 20. There will be other age groups living in the town, but most of its population will be centered around that age. 

The U.S. Census Bureau conducts a census every 5 years, in years ending in "2" and "7." This census, authorized by Title 13 in the U.S. Code, requires participation of all state and local governments in the United States. The first national census occurred in 1957.

The dependency ratio of a country reflects the number of people in a country whose labor supports the rest of the country that is incapable of working. It is usually determined by adding the number of retired people and children on one side, and the number of working adults on the other. In a country where the population is aging, like Italy and much of Northern Europe, the dependency ratio is growing as fewer and fewer people are supporting more and more retirees. Some geographers would argue that this is “unsustainable,” but there is as of yet insufficient evidence to conclusively say this is true.

In recent years, many politicians, scientists, and activists have raised the issue of the environmental changes to the Earth being caused by human consumption of resources. Almost all informed individuals agree that such extensive consumption and population growth cannot continue without dire consequences. While people in the developed world tend to decry overpopulation and rapid population growth as the main cause of environmental problems in the world, most politicians and activists in the developing world blame the disproportionate consumption of resources by the developed world.

The “dependency ratio” refers to the percentage of people within a population who are either too young or too old to work and must therefore be supported by the labor of working adults within that population. As the “baby boomers” continue to age, they exacerbate the burden on the Social Security system and the average American worker. In the United States, this is somewhat tempered by immigration and the high natural increase rate of the immigrant population, but in some European countries, the problem could soon become disastrous if the aging of the population continues.

A population pyramid is used to show the percentage of the population who fit into various age groups. If a population pyramid is triangle-shaped that means the bottom section (where babies and children are represented) is bigger than the middle section (where working adults are represented), which is in turn bigger than the top section (where retired older people are represented). This means that much of the population is young and that the population is increasing rapidly. A country like Nigeria or Bangladesh would have a triangle-shaped population pyramid.