Humans live on a small percentage of the planet. The world contains seven times as many people today as it did two centuries ago. Population density has increased significantly. However, population distribution has not. The vast majority of growth has been in areas already settled. For example, eastern China was one of the most populated parts of the world in 1800-and it still is today. Why have people chosen to live in such crowded places?

Where People Live

People want to live in places where they can survive with relative ease and comfort-places where they can raise or obtain food and live in moderate climates. Around 1800, when the population was only one billion, people were dispersed throughout such desirable lands. As population increased, the amount of suitable land stayed about the same, so people chose to live in greater densities on that same land.

Human geography tries to explain why people live where they do. It includes the study of two distinct but related concepts:

• Population distribution is the pattern of human settlement- the spread of people across the earth. Representing it on a map highlights places that are crowded, sparsely settled, or even empty.

Population density is a measure of the average population per square mile or kilometer of an area. It measures how crowded a place is. Understanding both population distribution and density helps people make important decisions on issues such as where to set the boundaries of an electoral district or where to develop new housing. These are among the many issues influenced by the number, distribution, and density of current and projected populations.

Physical Factors Influencing Population Distribution

Survival for the earliest humans depended on food, water, and shelter. Thus, these hunter-gatherers settled where these features were most readily available. Similarly, people today have the same basic needs, which helps explain why the population distribution has remained so similar over time. The map of Earth’s population distribution today below shows where the highest densities and largest numbers of people live today.

Midlatitudes

Most people live in the midlatitudes, the regions between 30 degrees and 60 degrees, north and south of the equator. These areas have more moderate climates and better soils than do regions at higher or lower latitudes. This pattern is particularly noticeable in the northern hemisphere because it includes more land than the southern hemisphere.

Low-Lying Areas

Most people live in low-lying areas rather than high-altitude areas, such as mountains. Low-lying areas typically have better soils for raising crops than do upland or high-altitude areas. In addition, these areas are often close to oceans, which facilitate transportation, provide a source of food, and have a moderating effect on temperature. Oceans keep the land warmer in the winter and cooler in the summer.

Other Factors

Most people live near lakes or rivers. People need fresh water to drink, and they can use it for irrigation, transportation, and to provide food. Regions of the world where it is difficult for humans to live typically have low population numbers and densities. These include mountainous areas, deserts, and high latitude/cold climates where agriculture is challenging. Lower population densities are also found in the tropics where disease is more prevalent and poor soils make farming difficult. Polar regions have no permanent human populations.

Human Factors Influencing Population Distribution

The places humans first settled included natural features that attracted them. However, then people themselves became an attraction. Newcomers moved in for safety, to find a job, or to be with friends or relatives. The populations and densities of cities have continued to grow, often to extreme levels.

Where people place transportation networks also has a significant impact on population distribution. People prefer to live close to trade routes. Roads, train lines, and rivers often produce a linear settlement pattern in which houses and communities stretch out in a line.

Political decisions sometimes bring clusters of populations to isolated locations where physical attributes would not normally attract settlement. For example, in 1950, Canada wanted a military base that could monitor possibly hostile actions by the country then known as the Soviet Union. So, it established a military base named Alert on the northern edge of its territory, in a land of ice, snow, and bitterly cold temperatures. Alert remains the most northerly community in the world.

Scale of Analysis and Physical Factors

The basic principle that people want to live on the most desirable land applies at any scale, or level of analysis by size. (See Topic 1.6 for more on scales of analysis.) As the scale of analysis changes, the relevance of certain factors such as climate, elevation, and industrialization changes as well.

At the global scale, regions with very high elevations-mountainous regions such as in the Himalayas, the Andes, and the Rocky Mountains-have cold climates, so such places usually have limited populations. However, elevation is sometimes important at the city level. People might prefer living at the highest elevations in a city because these spots offer cool breezes, safety from floods, and inspiring views of the landscape. At a regional scale, climate can also explain population distribution of a state such as California, where climate varies greatly within the state. For example, coastal California has a very large population compared to the desert and mountain regions of the interior. On a larger or local scale, such as a city, the spatial climate variation is usually too small to affect settlement.

Scale of Analysis and Human Factors

Polluted air is a health hazard, yet it may signal industrialization, economic development, and employment opportunities. On a global or national scale, millions of people are attracted to cities in search of economic opportunities and they might knowingly move to a polluted area. At a local scale, few people intentionally choose to settle near a pollution source unless they have to live there because lower property values make it more affordable.

Governments also have a significant influence on population distribution at different scales. A national government might increase the population of an area by building a new military base. A state might reduce population in an area by creating a new state park. A city government might affect population distribution by allowing high-rise apartment buildings in some areas and reserving other areas for single-family homes. (See Topic 6.6.)

Factors influencing a city’s population distribution such as elevation, proximity to desirable land, and land use laws commonly result in a population distribution that reflects social stratification-the hierarchical division of people into groups based on factors such as economic status, power, and/or ethnicity. Cities are characterized by regions and neighborhoods where the local population shares a characteristic that distinguishes it from other neighborhoods. For example, a neighborhood with large homes and parks would be likely to have families with children and an industrial zone might have few residences. In most countries, stratification is largely based on wealth, but sometimes policies and cultural beliefs have limited the areas where certain groups of people can live.

Population Density

Population density is calculated by comparing the area’s population to its size, and is expressed in the number of people per square mile or square kilometer. Demographers, people who study human populations, identify three types of population density: arithmetic, physiological, and agricultural.

Arithmetic Population Density

The most commonly used population density is the arithmetic population density, calculated by dividing a region’s population by its total area. In 2019, the United States had a population of approximately 328,239,523 in a total area of 3,841,999 square miles. Therefore, its arithmetic population density was 85.4 people per square mile, or 35.9 people per square kilometer. These figures are given in various styles. Two common styles are 85.4/sq. mi. and 85.4/mi?. But arithmetic density says little about population distribution. Population density is simply an average number of people overall in an area. It does not indicate where in the total area they live. The diagram below shows three areas with ten people per square mile, but with different distributions:

• In A, people are evenly dispersed throughout the area. This pattern is common in areas where each person or household lives on a large plot of land. At different scales and with different numbers, this basic pattern appears in many suburbs and many farming and ranching areas.
• In B, people are clustered, or nucleated, in one part of an area. This is a common pattern when people live near a central feature, such as a church, or are concerned about defense.
• In C, people are spread out in a line, known as a linear pattern. This pattern is common for people who live along a river or transit route.

Physiological Population Density

Another measure is physiological population density, calculated by dividing population by the amount of arable land, or land suitable for growing crops. Egypt (with 2.8 percent arable land), for example, recently had a physiological density of 8,078/sq. mile (3,156/sq. kilometer) compared to an arithmetic density of 226/sq. mile (88/sq. kilometer).

Such a large difference between the arithmetic and physiological densities indicates that a small percentage of a region’s land is capable of growing crops. Egypt’s high physiological density suggests a need for greater crop yields or for other food sources. The physiological population density is a much more useful measure than the arithmetic density to determine a region’s carrying capacity-the population it can support without significant environmental deterioration. (See Topic 2.2 for more about carrying capacity.)

A country with a high physiological density indicates that it needs high crop yields, but higher yields are not always possible. Many regions rely on imported food. Egypt and Japan both have physiological densities greater than 8,000 people/sq. mile of arable land. In both countries, growing enough food to feed the nation’s population is not practical with current technology. Both supplement crops through the fishing industry and with imported food. Paying for imported food is easier for a developed country, such as Japan, than it is for a less-developed country, such as Egypt.

In the table below, notice the relationship between the percent of arable land in a country and the difference between the arithmetic and physiological densities.

Agricultural Population Density

The third type of population density, agricultural population density, compares the number of farmers to the area of arable land. This value gives an indication of the efficiency of the region’s farmers. Developed countries have lower agricultural densities because farmers have resources and technology to produce large quantities of food with few workers. The agricultural densities in less-developed countries are higher because farmers often cannot afford modern technology, so they depend more upon labor. As a result, farmers in these areas are not able to produce as much food per farm worker.

Comparing all three types of population density for Bangladesh and the Netherlands provides insight into their demographic characteristics. Both countries exhibit high arithmetic densities, with Bangladesh at 2,914/sq. mi. and the Netherlands at 1,044/sq. mi. Similarly, they both demonstrate high physiological densities, with Bangladesh at 4,938/sq. mi. and the Netherlands at 3,505/sq. mi.

However, their agricultural densities starkly differ due to their distinct levels of economic development. The Netherlands, being more economically developed, boasts a low agricultural density of 31/sq. mi. This suggests that Dutch farmers can afford advanced technology and operate more efficiently compared to their counterparts in Bangladesh, where the agricultural population density is 431/sq. mi. Furthermore, the Netherlands’ advanced development enables it to import food that cannot be locally produced, further alleviating the pressure on agricultural resources.

Population density also exhibits temporal variations and varies across different scales of analysis. For instance, warm-weather states like Arizona and Florida experience increased population density during the winter months as “snowbirds” from northern states migrate to escape cold weather conditions.

At a local scale, time influences population density dynamics, as seen in the fluctuating population density of Manhattan, New York. With a resident population of approximately 1.5 million, Manhattan experiences a significant surge in population during weekdays, swelling to about 3 million as commuters flock into the city for work. This variability poses challenges for Manhattan’s infrastructure and service provision, as it must accommodate a transient population that contributes to its daytime density but resides elsewhere at night. Despite residing outside Manhattan, these commuters often contribute to the city’s tax base, which funds public services in both Manhattan and their residential areas.

Consequences of Population Distribution

Population density and distribution are intricately linked, shaping the characteristics and dynamics of regions across various scales, from countries to cities. Uneven distribution patterns lead to varying population densities, with some areas being densely settled and others sparsely settled. The implications of such distribution patterns are significant, particularly concerning their environmental impact and the effects of human activities.

In densely populated areas, human presence exerts a substantial impact on the natural environment. High-density regions often experience heightened environmental pressures due to factors such as resource consumption, waste generation, and urbanization. Conversely, sparsely populated areas typically witness fewer environmental disturbances as human activities are less concentrated.

The distribution and density of population reflect societal choices and values. Individuals’ preferences regarding living environments, whether urban or rural, are reflected in settlement patterns. Economic, political, and social processes are deeply intertwined with population distribution and density. Economic activities, for instance, gravitate towards densely populated areas where there is a larger customer base and access to a skilled labor force. Urban centers attract businesses and residents seeking economic opportunities, social amenities, and educational resources.

Political processes are also influenced by population distribution and density. Electoral boundaries are adjusted periodically to ensure equitable representation, with population shifts necessitating redistricting efforts. This process aims to maintain proportional representation by adjusting electoral districts based on census data. As urban populations grow while rural populations decline, redistricting often results in smaller urban districts and larger rural districts to uphold democratic principles of equal representation.

Overall, population distribution and density play crucial roles in shaping societal, economic, and political landscapes, reflecting and influencing the choices, values, and dynamics of human societies.

Population characteristics profoundly influence the availability and location of government and private services within a region. Essential facilities such as schools, police stations, fire stations, social assistance offices, and hospitals are strategically positioned near population centers to ensure accessibility. Each of these facilities serves as a central hub, surrounded by its functional region, catering to the needs of the local populace. Urban areas, characterized by higher population densities, boast a greater concentration of such facilities compared to rural areas, where basic services may be scarce, necessitating travel over long distances for access.

Infrastructure plays a pivotal role in supporting urban services and facilitating daily activities. Infrastructure encompasses various facilities and structures like sewer systems, electrical grids, and transportation networks. As cities expand, the demand for infrastructure increases, driven by the growing population. Higher population densities in urban centers, often fueled by preferences for city living, result in the construction of high-density housing units such as apartment complexes and condominiums. These densely populated neighborhoods, like Chicago’s Loop, accommodate a large number of residents within a small area, facilitating cost-effective service provision.

Providing services like sewerage, water supply, and law enforcement is more economically viable in high-density areas due to economies of scale. Infrastructure costs, such as laying sewer pipes, are primarily determined by labor expenses rather than the size of the population served. However, high-density areas present challenges such as increased susceptibility to contamination outbreaks and the rapid spread of diseases in crowded environments, underscoring the importance of effective management and sanitation measures.

Population distribution and density also influence environmental sustainability and resource management. Overpopulation, exceeding a region’s carrying capacity, can strain resources and exacerbate environmental degradation. Regions with favorable natural attributes may support larger populations sustainably, whereas those with limited resources may struggle to accommodate large populations. Thus, maintaining a balance between population growth, resource availability, and environmental conservation is essential for sustainable development.

The carrying capacity of a region is not static but can change over time due to various factors. Technological advancements in agriculture, such as the development of drought-resistant crops or improved irrigation techniques, can enhance a region’s ability to support a larger population by increasing agricultural productivity.

Climate changes also play a significant role in altering the carrying capacity of different locations. Regions with variable or marginal climates, like the Sahel in Africa, have experienced fluctuations in their carrying capacity due to changes in precipitation patterns. Areas once capable of supporting thriving populations may face challenges like droughts, leading to a strain on resources and exceeding the region’s carrying capacity without external assistance.

Cities, despite being built on land with varying carrying capacities, often emerge and thrive on land with optimal agricultural potential. Throughout history, settlers have been drawn to areas with fertile soil and ample natural resources, where they establish settlements that evolve into bustling urban centers.

Population density profoundly influences the environment, contributing to issues such as air and water pollution and resource depletion as urbanization progresses. High population density exacerbates environmental problems, leading to challenges like contaminated water sources and the need to import water from distant locations. Cities worldwide, including Cairo, Cape Town, Moscow, Bangalore, Beijing, and Jakarta, grapple with water scarcity issues, posing threats to economic development and population growth. Similarly, cities in the United States, such as Los Angeles, Houston, Atlanta, and Miami, face similar challenges, highlighting the critical importance of sustainable resource management and conservation efforts in densely populated areas.