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Gravity Model – AP Human Geography

Feb 25, 2022

If you plan to prepare for the AP Human Geography exam, it is crucial to learn about the gravity model to comprehend urban geography better. 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. This law applies to the gravity model because it identifies the contact strength between geographical regions such as metropolitan areas, cities, countries, etc. Furthermore, it aids in a greater understanding of the dispersion and size of towns and practical explanations of network interactions between them.


To understand the Gravity model AP human geography in detail, we will study Newton’s city planning law, explanations, examples, and historical implications. But first, let’s begin with a brief understanding of Newton’s law to answer what is the gravity model AP human geography.

Newton’s Law of City Planning

Sir Isaac Newton was a 17th century English mathematician, physicist, astronomer, alchemist, theologian, and author. He helped construct the guiding laws by which we know the interactions of the Universe by practically inventing the science of physics. The law of gravity, for example, stipulates that any two objects exert a pull of gravity on each other, which is directly proportional to their masses and inversely proportional to the square of the distance between them. The larger and closer two objects are, the more their gravitational pull will be.


But how does it relate to human geography? Can we push enough people into one location to boost a city’s gravitational pull? It’s similar, but not precisely like Newton described it. Besides, we can use Newton’s theories as a framework to understand the link between geographical places. Human settlements, such as towns and cities, impact each other based on size and distance, just as celestial entities do. It is known as the Gravity model AP human geography

History Of The Gravity Model AP Human Geography

Initially, the model was solely used to calculate the migration between two places. But today, the implication has been lengthened to show the flow structure of many items. Whether commodities or money flow from one location to another, this gravity can calculate the strength of all such interactions.


The intensity of the interaction corresponds to the population of each town and inversely corresponds to the distance between them. When this size is squared, the greater the association is between the towns, the more powerful the interaction is, and it’s precisely the opposite when the cities are far from each other. The latter relationship is considered distance decay. This is based on the idea that their interaction decays as the separation between two locations decreases.

Now you must be wondering what a basic kinematic Newtonian physics equation has to do with the Gravity model AP human geography and how and why does it apply?


This makes sense when opposed to primary objects in Newtonian kinematics since the physical force applied on one another is determined by the size of each entity and the spacing between them. Similarly, the size of each town and its proximity are the essential factors in determining how closely the cities are linked.

Illustrations Of The Gravity Model With Examples

There are various implications of the gravity model. Let’s look at some of them to answer “What is the gravity model AP human geography” more clearly.  


Suppose there are two pairs of cities. One team consists of large cities that are kept far apart, and the other is small towns held nearby. Let’s assume the first pair to be London and New York and the second to be Brussels and Amsterdam. It will help us comprehend the examples better. 

New York City has an estimated population of 8.5 million people, whereas London has an estimated population of 8.2 million people as of July 2016. They are at a distance of 3,470 miles. Amsterdam has 800,000 people, while Brussels has a population of 1.2 million. The distance between these two towns is 109 miles. Don’t worry! If you plan to sit for the AP exam, you don’t have to do any math. This is only to prove the model’s implications.


Now let’s calculate the strength of interaction between both pairs. This first pair’s strength is 5,788,604, and the second pair’s strength is 80,801,279.

This shows that, while city population impacts how important a city is in terms of push-pull variables and interaction strength with other towns, distance is a broader factor (hence it is being squared). For example: Although New York and London are two of the world’s biggest and most prosperous cities, they have low intensity due to their far distance. But Amsterdam and Brussels are relatively minor, as they are nearer to each other, which has created a power that is approximately 32 times more powerful than New York City and London.

Weaknesses Of The Gravity Model

While the Gravity model AP human geography provides a decent idea of the connection between the two cities and how readily traffic flows between them, it has significant flaws. Let’s study the defects to understand the depth of the gravity model AP human geography

  • The first weakness is that there is debate over whether the distance term should refer to the actual geographic radius or the available length, which refers to the miles covered by road, rail, or air. Critics believe that each assessment will change the total flow and interaction strength. People traveling between New York and London, for example, would have different functional distances than information transmission, which involves integrating the journey with satellites.
  • Another flaw is that the units’ interaction strength isn’t stated in the Gravity model AP human geography. This is because the units generated by this computation are meaningless, but a gravitational constant is provided in the Newtonian gravity model to give the calculation a physical significance. As a result, critics contend that it is not scientifically valid and relies solely on observation.
  • The third flaw is that the model mentions the distance beforehand, not calculating the physical and political geography. 

To understand physical geography, let’s take another example. Let’s take Houston city and compare its distance with Mexico and New York. 

Within the city borders of Mexico City, there are around 9 million inhabitants, somewhat more than in New York. Let’s presume the difference is insignificant for the sake of comparison. On the other hand, New York City is roughly twice as far away from Mexico City and Houston. This suggests that Houston and Mexico City flow is approximately four times more frequent than movement between Houston and New York City. For a variety of reasons, we know this isn’t the case. 

The fundamental reason is that to get to Mexico City from Houston, we must cross political borders, which we do not have to do when visiting New York City. Furthermore, due to the political context in Mexico City, conditions are significantly worse than in New York City, making movement less possible in this situation.

Let’s use the same example in physical geography. Here, we can assume the physical feature to be something like mountains or harsh terrain that acts as a hindrance. Although there are many methods to change and adjust the gravity model to give a more realistic flow view, it still does a great job of providing a complete picture of how flow happens between two sites. The gravity model has been utilized for years and will likely be used even in the future to understand how and why flow happens between certain places and the size.


The Gravity model AP human geography concept is derived from Newton’s Law of Gravitation. It takes two cities and measures their interaction intensity based on their populations and distances. Due to the idea of distance decay, the stronger the interaction is, the farther away the cities are, and it happens the opposite when the interaction is low. Although this model is a decent predictor of interaction, it has several flaws; the most significant is its inability to account for specific variables. But even then, it is one of the most efficient gravity models, which will continue to serve many people in the future for conducting the above calculations.  

gravity model ap human geography


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