Gravity Model: AP® Human Geography Crash Course Review | Albert.io (2022)

Introduction to the Gravity Model

When discussing urban geography, more particularly cities and urban land use, it is important to understand the gravity model, as we will discuss in this study guide. The gravity model helps to give a clearer understanding of the distribution and size of cities while also providing useful explanations of interactions among networks among cities.

To understand a gravity model definition, you should understand that it is called the gravity model because it is related to Isaac Newton’s Law of Gravitation, which predicts the gravitational force between two objects. Newton’s Law is applied to urban geography in the sense that it determines the strength of the interaction between two urban geographical regions, which can be cities, metropolitan areas, countries, etc. The strength of this interaction can be calculated by the formula below:

S=\dfrac { { P }_{ 1 }{ P }_{ 2 } }{ { D }^{ 2 } }

where { P }_{ 1 }and { P }_{ 2 }are the populations of cities 1 and 2, respectively, D is the distance between the two cities, and S is the interaction strength. The populations are, of course, in units of people, and the distance is generally in units of miles or kilometers, depending upon where in the world you are. The resulting strength is, therefore, in units of { people }^{ 2 }/{ mi }^{ 2 }or { people }^{ 2 }/{ km }^{ 2 }. However, the number is usually just reported without units.

To explain the mathematical relationship, it is the strength of the interaction between two cities (we will assume they are cities for the sake of simplicity for this article, although you should still keep in mind that it could refer to any political or geographical subdivision) is determined by multiplying the population of one city by the population of the second, dividing by the square of the distance between the two cities.

The strength of the interaction between the two cities determines flow between the two cities. Initially, this was used only to account for migration from one place to another. However, the model has been expanded to show that it may explain different types of flow. These various types of flow could be of people, information, commodities, money, labor, and pretty much anything else that moves between two locations. The interaction strength is directly proportional to the population of each city and inversely proportional to the square of the distance. The larger the cities, the stronger the interaction, and the farther the cities are from one another, the weaker the interaction is, with this magnitude being squared. The latter relationship is known as distance decay, which refers to the idea that as distance decreases between two places, so does the interaction in an exponentially decaying manner.

(Video) Gravity Model and Migration (AP Human Geography)

How and why does a fundamental kinematic Newtonian physical equation apply to human geography? When compared to physical objects in Newtonian kinematics, this makes sense because, in that context, the size of each object and distance between objects determines the physical force exerted on one another. In the same way, the size of each city and the distance between them are the primary determinants of how closely the cities are bound together.

Example and Explanation of the Gravity Model

Gravity Model: AP® Human Geography Crash Course Review | Albert.io (1)

So that you can better see how this works let’s look at an example of two pairs of cities, with one being a pair of the large cities far apart and the other being a pair of smaller cities closer together. In the first pair, we will look at New York City and London, and in the second pair we will look at Amsterdam and Brussels.

As of July 2016, the population of New York City is approximately 8.5 million people and London is 8.2 million people. They are 3,470 miles apart. The population of Amsterdam is approximately 800,000 people and Brussels is 1.2 million people. These two cities are 109 miles apart. Don’t worry, you won’t have to do actual calculations on the AP® exam. This is just to show the implications of the model.

First, let’s calculate the interaction strength between New York City and London, which is 5,788,604. Next, we will do the same for Amsterdam and Brussels, which is 80,801,279.

This shows that although the population of cities determines how important a city is, regarding its push-pull factors and its interaction strength with another city, it is not as strong a factor as the distance is (hence it being squared). Even though New York City and London are two of the largest and most influential cities in the world, while Amsterdam and Brussels are significantly smaller, the fact that Amsterdam and Brussels are much closer to one another than New York City and London has created an interaction strength that is approximately 32 times stronger.

While the gravity model gives a good understanding of the relationship between the two cities and how easily flow occurs between them, there are several weaknesses to the model. The first is that people argue whether, for the distance term, to use the actual geographic distance between two places or to use what is known as the functional distance, which refers to the distance by way of roads, rail, or flights. However, if accounting for overall flow and interaction strength, the functional distance for each measurement would be different. For example, between New York and London, the functional distances would be different for people flying, as opposed to information transmittance, which requires integrating the distance to satellites.

Another criticism of the gravity model relates to the fact that the interaction strength isn’t represented in units. This is because the units resulting from this calculation are physically meaningless while, in the Newtonian gravity model, a gravitational constant is included to give the calculation physical meaning. Therefore, the criticism argues that it is not scientifically verifiable and can only be based on observation.

(Video) APHG.2.9- How does the Gravity Model predict the movement of goods & people?

Also, it makes a sweeping assumption that we know not to be true. It assumes that distance is included in the model regardless of political and physical geography. Obviously, there will be different boundaries that need to be crossed in this regard.

Looking at political geography, let’s take a city like Houston and compare it with Mexico City and New York City. Mexico City has a population of approximately 9 million people within the city limits, slightly higher than that of New York. For the sake of comparison, let us assume that the difference is negligible. However, New York City is approximately twice as far from Houston as Mexico City. This means that flow is nearly four times more likely to occur between Houston and Mexico City than between Houston and New York City. We know that’s not true for several reasons. The main reason is that to get to Mexico City from Houston, we need to cross political boundaries, something we don’t need to do if traveling to New York City. Also, conditions are far worse in Mexico City due to political climate, than in New York City, making flow less likely in this situation.

We can apply the same example to physical geography in that there could be a physical feature that acts as a hindrance, such as mountains or rough physical terrain.

Although there are plenty of ways in which the gravity model can be improved and adjusted to provide a more realistic picture of flow, it still does an excellent job giving an overall picture of how flow occurs between two points. The gravity model has been used for years and will continue to be used to understand how and why flow occurs between certain areas and to what magnitude.

The Gravity Model and the AP® Human Geography Exam

On the AP® Human Geography course description, the idea of the gravity model falls under the category of “Cities and Urban Land Use.” More specifically, you would be asked to use the gravity model to study systems of cities, while focusing on the location of cities, and why cities are where they are. You most likely will not be asked specifically what the gravity model is but rather you will be asked how you can apply it to certain scenarios.

On the AP® Human Geography multiple choice part of the exam, it would be difficult to incorporate the gravity model without it being a straight gravity model definition question. Therefore, you’re far more likely to use it in the free-response question (FRQ) section than in the AP® Human Geography multiple choice section. You would use it on the AP® Human Geography FRQ as a tool to explain a phenomenon that the question is asking.

To help you apply this study guide to the exam as best as possible, here is an example of an AP® Human Geography FRQ from the 2008 AP® Human Geography Exam (Question 2):

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Gravity Model: AP® Human Geography Crash Course Review | Albert.io (2)

Regional migration patterns within the contiguous United States are the result of several factors. The map above shows net migration at the county level, but these data support generalizations about migration patterns at the regional scale.

A. Identify two specific regions that have experienced net in-migration.

B. Identify two specific regions that have experienced net out-migration.

C. Explain the processes that contribute to the general patterns of migration within the United States shown on the map in terms of each of the following:

1. Economic structure

2. Friction of distance

3. Age structure of the population

(Video) CRASH COURSE: AP human geography exam review (Part 1)

You would use the gravity model in part C of this question while addressing the friction of distance. Here, you would say that areas of in-migration are directly related to the gravity model because there is a high amount of interaction between the places. Therefore, people begin to migrate there due to the fact that the magnitude of interaction is higher.

Wrapping up the Gravity Model

To wrap up this section of the study guide, the gravity model definition derives itself from Newton’s Law of Gravitation, and essentially takes two cities and determines the strength of interaction between them by using their populations and distances. The higher the populations, the stronger the interaction, and the farther away the cities are, the lower the interaction is squared, due to the idea of distance decay. Although this model is a good indicator of interaction, some weaknesses mostly pertain to its inability to account for certain variables. You would most likely be asked to use this on the AP® Human Geography FRQ section as a tool to explain certain phenomena related to migration patterns. It is unlikely that you will be asked about this on the AP® Human Geography multiple choice portion of the exam.

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FAQs

What is the gravity model AP Human Geography? ›

The Gravity Model holds that the interaction between two places can be determined by the product of the population of both places, divided by the square of their distance from one another. The primary implication of this model is that distance is not the only determining factor in the interaction between two cities.

What is the gravity model AP Human Geography example? ›

Gravity Model: The movement of people between two places is based on factors of population size and distance. For example, a big city like Chicago is likely to attract commuters from a fairly large radius because of its size, but the further away you get, the more likely people are to travel to other cities such as St.

What does the gravity model predict? ›

The gravity model of international trade predicts that the flow of goods between two locations is positively related to their size (or income levels) and negatively related to the distance between them, after controlling for factors that may affect trade (e.g., price differences and differences in the salient features ...

Who created the gravity model AP Human Geography? ›

Thus, this article will discuss urban geography, especially city and urban land use, to clarify this gravity model. But before we move further, it is essential to know that Issac Newton has formulated this gravitational model. According to Newton's law of gravitation, gravitational pull acts between two objects.

How is the gravity model used? ›

Gravity models provide an intuitive framework to understand the determinants of flows between countries, in particular: trade, migration, or capital. Gravity models can easily be derived from theoretical models such as random utility maximization models.

How does the gravity model predict the movement of people? ›

The gravity model of migration is therefore based upon the idea that as the importance of one or both of the location increases, there will also be an increase in movement between them. The farther apart the two locations are, however, the movement between them will be less. This phenomenon is known as distance decay.

What is an example of the gravity model? ›

If we compare the bond between the New York and Los Angeles metropolitan areas, we first multiply their 1998 populations (20,124,377 and 15,781,273, respectively) to get 317,588,287,391,921 and then we divide that number by the distance (2462 miles) squared (6,061,444). The result is 52,394,823.

What are the weaknesses of the gravity model? ›

Another criticism of the gravity model relates to the fact that the interaction strength isn't represented in units. This is because the units resulting from this calculation are physically meaningless while, in the Newtonian gravity model, a gravitational constant is included to give the calculation physical meaning.

What are the two patterns common to the gravity model? ›

The theoretical principle of the gravity model is twofold: (1) the degree of interaction is directly proportional to the size of the masses and (2) the degree of interaction is indirectly proportional to the distance that separates them.

What is one criticism of the gravity model? ›

One criticism of the gravity model of international trade is that it takes no account of comparative advantage. This critique is particularly important when the gravity model is considered for policy applications such as identifying priority markets for trade promotion programs.

What are the assumptions of gravity model? ›

Gravity models assume that flows between two countries are directly proportional to their size (population or GDP) and are inversely proportional to the physical distance between them (similar to Newton's gravitational law).

How the gravity model explains international trade? ›

The gravity model of international trade in international economics is a model that, in its traditional form, predicts bilateral trade flows based on the economic sizes and distance between two units. Research shows that there is "overwhelming evidence that trade tends to fall with distance."

Who invented gravity model of migration? ›

Thus, the 'law' of spatial interaction in human behaviour (see also e.g. Anderson, 2011) resembles Newton's 1687 law of gravity. The idea of applying a physics law to population movement between two locations was first formally advocated by John Q. Stewart who established the 'social physics' school (Stewart, 1950).

Why is the gravity model so popular in trade research? ›

It is intuitively appealing, and also happens to have very strong explanatory power. The gravity model accords well with basic intuition about the drivers of international trade. It does a good job of explaining some important stylized facts about international trade.

What is gravity modeling? ›

The gravity model of international trade states that the volume of trade between two countries is proportional to their economic mass and a measure of their relative trade frictions. Perhaps because of its intuitive appeal, the gravity model has been the workhorse model of international trade for more than 50 years.

How do you find the friction factor in gravity model? ›

Gravity Model - YouTube

Which phase of planning uses gravity model? ›

The Use of Gravity Model in Spatial Planning.

What are the factors that determine the pattern of international trade as identified by the gravity model? ›

Gravity model is derived from physics and is used to explain the bilateral flow of trade determined by GDP per capita, population, and distance. It is assumed that trade flow between the two countries is positively related to their economic size and population.

Why is the gravity model important? ›

A gravity model provides an estimate of the volume of flows of, for example, goods, services, or people between two or more locations. This could be the movement of people between cities or the volume of trade between countries.

Which one of the following statements correctly explains the difference between gravity model and potential model? ›

The main difference between the two models is Gravity model deals with only two places at a time, while the Potential model accounts for interactions between many places.

How has gravity model been used in various activities of spatial activity? ›

Gravity like representations have been applied in a wide variety of contexts, such as migration, commodity flows, traffic flows, commuting, and evaluating boundaries between market areas.

Does the gravity model predict or explain Namibian exports? ›

The purpose of this study is to investigate factors that determine exports of Namibia using a gravity model approach. The analysis indicates that increases in importer's GDP and Namibia's GDP cause exports to increase, while distance and importer's GDP per capita are associated with a decrease in exports.

Why gravity model is get calibrated? ›

Before the gravity model can be used for prediction of future travel demand, it must be calibrated. Calibration is accomplished by adjusting the various factors within the gravity model until the model can duplicate a known base year's trip distribution.

How do you calibrate a gravity model? ›

Calibration of the gravity model involves adjusting the friction factor. The socioeconomic adjustment factor is an adjustment factor for individual trip interchanges. An important consideration in developing the gravity model is "balancing" productions and attractions.

What are the two main variables in the gravity model Mcq? ›

Two main variables in the gravity model. Relationship between distance and interaction. Highest degree of interaction between two places.

What are the three trade barriers? ›

The major obstacles to international trade are natural barriers, tariff barriers, and nontariff barriers.

Who gave the theory of mercantilism? ›

Adam Smith coined the term “mercantile system” to describe the system of political economy that sought to enrich the country by restraining imports and encouraging exports. This system dominated Western European economic thought and policies from the sixteenth to the late eighteenth centuries.

What are the major trade barriers to export and import? ›

The barriers can take many forms, including the following:
  • Tariffs.
  • Non-tariff barriers to trade include: Import licenses. Export control / licenses. Import quotas. Subsidies. Voluntary Export Restraints. Local content requirements. Embargo. Currency devaluation. Trade restriction.

What is Lee theory of migration? ›

Lee's migration model is a model that accounts for push/pull factors and intervening obstacles in order to predict migration patterns. It advocates the idea that intervening obstacles can block migration to certain areas, while push and pull factors can promote migration out of an old area to a new one.

Which theory is also known as 2 2 2 Model? ›

The original Heckscher–Ohlin model contained two countries, and had two commodities that could be produced. Since there are two (homogeneous) factors of production this model is sometimes called the "2×2×2 model".

What are the most important determinants of bilateral trade flows? ›

These factors include political instability, membership in specific economic unions, and such cultural factors as religion and language. Second, the present study controls for variation in the size of nations' economies.

Why is gravity model important? ›

A gravity model provides an estimate of the volume of flows of, for example, goods, services, or people between two or more locations. This could be the movement of people between cities or the volume of trade between countries.

How is the gravity model calculated? ›

The gravity model can be calculated as the product of the population sizes, divided by distance squared, or S = (P1 * P2) / (D * D). What this shows is that the bigger and closer places are, the more influence they're likely to have on each other.

What is gravity model in international trade? ›

The gravity model of international trade states that the volume of trade between two countries is proportional to their economic mass and a measure of their relative trade frictions. Perhaps because of its intuitive appeal, the gravity model has been the workhorse model of international trade for more than 50 years.

Why is the gravity model so popular in trade research? ›

It is intuitively appealing, and also happens to have very strong explanatory power. The gravity model accords well with basic intuition about the drivers of international trade. It does a good job of explaining some important stylized facts about international trade.

What is one criticism of the gravity model? ›

One criticism of the gravity model of international trade is that it takes no account of comparative advantage. This critique is particularly important when the gravity model is considered for policy applications such as identifying priority markets for trade promotion programs.

What are the strengths of the gravity model? ›

The gravity model helps to give a clearer understanding of the distribution and size of cities while also providing useful explanations of interactions among networks among cities.

What are the limitations of gravity model? ›

The findings suggest that: (1) finer-scale urban mobility networks do not demonstrate a scale-free property; (2) the performance of the basic gravity model decays for predicting population flow in the finer-scale urban mobility networks; (3) the variations in population density distribution and mobility network ...

What is an example of the gravity model? ›

If we compare the bond between the New York and Los Angeles metropolitan areas, we first multiply their 1998 populations (20,124,377 and 15,781,273, respectively) to get 317,588,287,391,921 and then we divide that number by the distance (2462 miles) squared (6,061,444). The result is 52,394,823.

What are the two patterns common to the gravity model? ›

The theoretical principle of the gravity model is twofold: (1) the degree of interaction is directly proportional to the size of the masses and (2) the degree of interaction is indirectly proportional to the distance that separates them.

How do you find the friction factor in gravity model? ›

Gravity Model - YouTube

What are the two main variables in the gravity model Mcq? ›

Two main variables in the gravity model. Relationship between distance and interaction. Highest degree of interaction between two places.

Does the gravity model predict or explain Namibian exports? ›

The purpose of this study is to investigate factors that determine exports of Namibia using a gravity model approach. The analysis indicates that increases in importer's GDP and Namibia's GDP cause exports to increase, while distance and importer's GDP per capita are associated with a decrease in exports.

Who discovered gravity? ›

Sir Isaac Newton was born especially tiny but grew into a massive intellect and still looms large, thanks to his findings on gravity, light, motion, mathematics, and more.

What are the factors that determine the pattern of international trade as identified by the gravity model? ›

Gravity model is derived from physics and is used to explain the bilateral flow of trade determined by GDP per capita, population, and distance. It is assumed that trade flow between the two countries is positively related to their economic size and population.

Which theory is also known as 2 2 2 Model? ›

The original Heckscher–Ohlin model contained two countries, and had two commodities that could be produced. Since there are two (homogeneous) factors of production this model is sometimes called the "2×2×2 model".

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