# What is the difference between physiological density and agricultural density?

Remember the earlier comparison of Russia and Bangladesh? This is the section where we discuss the different ways of calculating the pressure that populations put onto the land that they inhabit. You’ll recall that we began by looking simply at people per country. This is a good way to start, but the limitations are fairly obvious. Countries that are physically larger can hold more people. We need to use a method that changes from a measure of overall population to some kind of per capita measure. There are many of these and each has its merits.
Arithmetic density is the simplest one. It is simply the number of people divided by the area of the country. The area is usually measured in square kilometers, since most of the world uses the metric system (Figure 2.17).

Figure 2.17 | Arithmetic Density 201514
Author | David Dorrell
Source | Original Work
License | CC BY SA 4.0
Physiological density has the same numerator (population), but the denominator is different. Instead of using all the land in a country, it only accounts for arable (farmable) land (Figure 2.18). Places that are not used for agriculture- deserts, lakes, mountaintops and similar places – are subtracted from the land total. This is useful for demonstrating how much pressure is being put on the farmland that is available. Be aware that food that is gathered or hunted from non-agricultural land is not considered in this number.

Figure 2.18 | Physiological Density 201515
Author | David Dorrell
Source | Original Work
License | CC BY SA 4.0
Agricultural density has the same denominator as physiological density, but has a different numerator. Instead of using the entire population, it only uses farmers (Figure 2.19). This provides a number that is a good measure of development, or rather it’s a good measure of underdevelopment. Developed countries have mechanized agriculture and few farmers per capita. Each farm tends to be large in order to generate a sufficient income. Places with high agricultural densities have more farmers per hectare, meaning that farms will likely produce less revenue. Of course, an underlying assumption of this number is the idea that people are growing food to earn a living. If they are eating the produce directly, outside the cash economy, then the comparison is less valid.

Figure 2.19 | Agricultural Density 201516
Author | David Dorrell
Source | Original Work
License | CC BY SA 4.0
Related to food production is the concept of carrying capacity. Carrying capacity is simply how many people can live from a given piece of land. However, it’s not really that simple. Carrying capacity is not static throughout time. Not only do environmental characteristics change (due to desertification, for example) but technology changes as well. The carrying capacity of land in wealthy developed countries has expanded tremendously due to the application of technology. These technologies could be something as simple as irrigation ditches to something as complex as genetic modification of the plants and animals themselves. Carrying capacity is snapshot taken at a particular time.

The physiological density or real population density is the number of people per unit area of arable land.

A higher physiological density suggests that the available agricultural land is being used by more and may reach its output limit sooner than a country that has a lower physiological density. Egypt is a notable example, with physiological density reaching that of Bangladesh, despite much desert.

Solution :  Physiological density is the number of people per unit of arable land. Agricultural density is the number of farmers per unit of arable land.
Agricultural population includes cultivators and agricultural labourers and their family members.

Huge country. Small population. High population density? How can that be? It all makes perfect sense once you realize we are measuring physiological population density and not arithmetic population density. The difference between the two makes a big difference!

## Physiological Population Density Definition

If you are a country with lots of deserts, a single river, and a large population that is growing quickly, we're probably talking about you.

Physiological Population Density: The ratio of people to farmland (arable land), usually applied to countries or country subdivisions.

## Physiological Population Density Formula

First, find the total population (P) of a unit of land (such as a county, state, or country).

Next, find the amount of arable land (A) within that unit of land. It will be either equal to or less in area than the unit of land.

Arable land is land that is farmed for crops, either actively or in rotation (i.e., is currently fallow but is part of a cropping system). Arable land does not include land that could theoretically be farmed but has not been converted to cropland, such as a forest. It also does not include pasture and grazing land unless part of a crop rotation system (in cases where animals are pastured on fallow cropland).

The physiological population density is P divided by A (P/A).

In the US, this is likely to be expressed as people per square mile, and in the rest of the world, as people per square kilometer or hectare.

Agriculture and farming, which include animal grazing, are often confused with cropland. Some measures of physiological population density may also consider population density in relationship to cropland AND grazing land. Meanwhile, agricultural population density considers the ratio of farms (and/or farms) to arable land.

## Difference between Physiological and Arithmetic Density

Arithmetic density gives us the population density across an entire area, whether cropland or something else.

In a completely agricultural region made up only of arable land, physiological and arithmetic density are equal. In areas with no cropland whatsoever, there is no physiological population density.

Fig. 1 - Rice farmers in Bangladesh. Sixty percent of Bangladesh's land area is arable, the highest ratio in the world (Ukraine is 2nd, India is 5th)

The difference between the two types of density is important in regions with both arable land and non-arable land. In this case, it can be very misleading to assume that arithmetic population density is accurate and helpful if we are trying to determine the relationship between people and food consumption.

Country X has an arithmetic population density of over 3000 people per square mile. Over 50% of the land in the country is arable, so can country X feed itself? Some figures state that a single person can survive for a year on crops from about half an acre (a large garden), and there are 640 acres in a square mile, so it looks like only 1450 people per square mile could be fed. Country X might not be self-sufficient in food, then. However, we used the figures for Bangladesh, which is self-sufficient in rice (its staple crop, which is highly productive/acre), an amazing achievement for a country once hit by famines.

Country Y has the same arithmetic density as Country X, but its physiological density is around 10000 people per square mile. Can it feed itself? Not with its arable land, since ten thousand people have to rely on each square mile of cropland. Country Y is very likely a net food importer, at least of its fruits, grains, and vegetables.

Meanwhile, Country Z has a physiological density of 10 people per square mile. Country Z is likely a net food exporter.

## Countries with High Physiological Density

Let's consider the top ten countries in the world in terms of their physiological population densities (PPD).

### The Top Ten

This eclectic list is 1) Singapore, 2) Bahrain, 3) Seychelles, 4) Kuwait, 5) Djibouti, 6) United Arab Emirates, 7) Qatar, 8) Maldives, 9) Andorra, and 10) Brunei.

Singapore, a wealthy city-state, has a PPD of 386100 people/square mile compared to an arithmetic population density (APD) of 18654 people/square mi, a huge difference. This is because of Singapore's total land area of 263 square miles, only two square miles are arable land.

Indeed, most of the above are quite small in area (UAE is 32000 square mi., but mostly desert), and thus obviously can't rely on their own crops for food. Five are desert countries, four of these wealthy emirates in Southwest Asia, and one, Djibouti, is a state based around a port in the Horn of Africa. They have close to no cropland, people live almost entirely in urban areas or are nomadic herders or fishermen, and national income is used to buy crops on the international market.

The Pyrenean micronation of Andorra survives on tourism revenue, as do the Indian Ocean nations of Seychelles and Maldives. Brunei is an oil-rich rainforest nation that protects its forests rather than turning them into farms.

In other words, these, and others farther down the list, aren't highly relevant to the concept of physiological density.

AP Human Geography requires that you understand the differences between the two types of population density and in which cases each is informative for demographic studies.

### Taiwan

Taiwan, at number 20 in the world, is the first country on the list for which the concept is quite useful. Taiwan's APD of 1849 people/square mile is a fifth of its PPD of almost 10000 people/square mile because much of Taiwan consists of high, steep mountains that are largely useless for crop cultivation. If you didn't know this, you might think Taiwan can feed itself. While its farming areas are critical to providing food for its population, Taiwan does not have nearly enough arable land to do so and relies heavily on food imports: it is equivalent to Country Y in the example above.

### The US

The US, at number 173 on the list, has one of the world's lowest physiological population densities. It is also number two in total arable land area in the world (after India, which has three times the population of the US), so, not surprisingly, like County Z in the example above, the US is a net food exporter. Indeed, the US exports more food, in volume as well as value, than any other country.

## Physiological Population Density Example

Wealthy desert countries such as Qatar and Bahrain have barely any cropland, but they can also afford to import what they need. Egypt, another desert country, is another story.

### Egypt

Egypt, with around 110 million people and growing rapidly, has a moderate arithmetic population density of 289 people per square mile, around that of France or Turkey, countries with little problem feeding themselves. However, Egypt's physiological population density is around 3500 per square mile, one of the highest in the world for non-city states. This isn't much higher than Bangladesh, but Bangladesh is a wet, tropical country with plenty of fresh water and no need for irrigation. Most of Egypt's population and crops can only exist along a narrow ribbon of land and water, the Nile Valley and Nile Delta.

Egypt depends on every square inch of available cropland and, outside a few oases, irrigation from the Nile.

Fig. 2 - Population density of Egypt's governorates (subdivisions) shows the contrast between the high concentration of population along the Nile, increasing to the north where more cities are located, and the extremely low densities of the desert

Before Egypt went through the demographic transition, farmers had large families, but populations grew quite slowly. Now, people still have large families, the population is growing rapidly, and little new farmland is available (though see below). Thus, people who stay in Egypt must find other trades, and their numbers tend to swell the cities. As urban areas grow larger and larger, buildings, roads, and other infrastructure overwhelm agricultural land, driving physiological population density even higher. Water becomes scarcer and scarcer. More and more people depend on the same amount of cropland. is there any way out of this debacle?

## Modifying Physiological Density

Physiological population density can be changed if non-arable land can be made arable. If you have ever flown over the US, you may have seen this in action. The semi-deserts of Nebraska's High Plains, underlain by the Ogallala Aquifer, pump fossil water from the last Ice Age to the surface to make land arable that otherwise would only be suitable for grazing.

### Making the Desert Bloom, but at What Cost?

Egypt can theoretically make the Sahara arable. This is not far-fetched: the Sahara, after all, was once a grassland in wetter times of the Earth's history. All that is needed now is water. But there is a catch (several, actually) to altering your physiological density by increasing your amount of arable land.

Irrigation needs water from somewhere. In Egypt, this could mean turning Red Sea or Mediterranean saltwater into freshwater, using water piped from the Nile, buying freshwater from another country, tapping into aquifers, or some combination. Here are the catches:

• Aquifers are problematic because, if they aren't recharged fast enough, often the case in deserts, they will run dry.

• Without rainwater to flush out mineral salts, avoiding salinization of irrigated soil can be difficult. Once salinization happens, agriculture is no longer an option.

• Desalinization of seawater only works for wealthy countries because it is an extremely expensive technology.

• Pipes from the Nile? This threatens the ever-growing need for freshwater in urban areas as well as existing agriculture along the Nile.

• As for neighbor countries, they are either in the same situation (e.g., Libya, Israel, Jordan, Saudi Arabia) or they are not on friendly terms (e.g., Sudan).

### Changing the Farm

What if we farmed desert plants or at least plants that don't need much water?

The farming of cacti, particularly the nopal or prickly pear (Opuntia), provides nutritious food as well as a cash crop.

Fig. 3 - The prickly pear or nopal is one of many species of cacti that grow as weeds in Mexico and elsewhere but are also farmed for their delicious fruit

### Farming the City

Traditionally, arable land has meant rural land where plants grow in soil. But what if we changed the definition of crops? What if they could grow on a wall, a road, or a vacant lot? Stacked up in layers...underground? Without soil? Welcome to the world of hydroponics, aeroponics, and other urban agriculture solutions.

The idea here is that cities can and should provide much of their own food. And why not? The majority of humanity lives in cities, and the proportion is steadily increasing. Yet cities are filled with spaces where food could be grown (and boy, would it cut down on transport costs!). French intensive gardening has existed in France's urban areas for over 500 years, after all. And in China, it is common to see vegetable gardens filling every available niche in cities.

### What is the difference between physiological density and arithmetic density?

Arithmetic Density: basic calculation of total number of people living in a particular geographical area of land. Also known as real density. Physiological Density: calculation of total number of people in a particular geographical area of arable land.

### What is physiological density?

Physiological density is the number of persons per unit of agricultural land. This measure of density is useful, because it can give us a rough estimate of how many people an area of farmland can reasonably support. Physiological density is also helpful when studying population pressure and overcrowding.

### What is an example of agricultural density?

Agricultural Density The ratio between the amount of arable land and the number of farmers. For example, the US has a low agricultural density because there is 1 farmer per square kilometre.

### What does agricultural density measure?

Answer and Explanation: Agricultural density is defined as the number of farmers per unit area of farmland. Agricultural density = (Total number of farmers) / (Total area of farmland) This measure yields the average area of land farmed by one farmer.