AP Human AP Human GeographyGeography

GRAVITY GRAVITY MODELMODEL

What is a model?What is a model?

a representation of some phenomenon of the real-world made to facilitate an understanding of its workings

a simplification and/or generalization of a complex reality from which the incidental detail has been removed

an abstraction – not a reality

Types of geographic models

Mathematical Graphic Textual

What do you need to know about models?

The associated geographer The “parts” of the model The “assumptions” of the model Critiques of the model Applications of the model

Most Critical!Most Critical!

A model IS NOT a “plan” to be followed in the future.

A model IS a “description” of what happened in the past.

A model IS NOT a critique of the present.

A model IS a pattern to which we can compare the present in order to see differences.

Tobler’s Law of GravityTobler’s Law of Gravity

Waldo ToblerWaldo Tobler "Everything is related to everything "Everything is related to everything

else, but near thing s are more else, but near thing s are more related than distant things.”related than distant things.”

Gravity ModelGravity Model Uses size of location Uses size of location

and distance as factors and distance as factors for travelfor travel

Size of location takes Size of location takes precedent over distanceprecedent over distance

The gravity model can The gravity model can be used to estimate:be used to estimate: Traffic Flows Traffic Flows Migration between two Migration between two

areas areas The number of people The number of people

likely to use one central likely to use one central place place

The GRAVITY MODEL of MIGRATION is a model, derived from Newton's law of gravity.

Newton's law states that: "Any two bodies attract one another with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them." 

The GRAVITY MODEL of MIGRATION is used to predict the degree of interaction between two places

When used geographically, the words 'bodies' and 'masses' are replaced by 'locations' and 'importance' respectively,.

Importance can be measured in terms of population numbers, gross domestic product, or other appropriate variable.

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.

o The farther apart the two locations are, however, the movement between them will be less.

o This phenomenon is known as distance decay.

The simplistic version of the gravity model of migration is as follows:

Mij = gravity model prediction of migration between origin i and destination jPi = population of origin State iPj = population of destination State jdij = distance from origin i to destination j

 Mij

= 

Pi*Pj

dij2

CITY POPULATION (2012)ATLANTA 443,775

NEW YORK CITY 8,336,697

KNOXVILLE 182,200AUSTIN 842,592

LOS ANGELES3,857,799CHICAGO 2,714,856

TULSA 393,987

COMPARE ATLANTA TO EACH OF THE CITIES LISTED

How might the calculations of distance you came up with differ from actual travel distances in real life?What other factors might influence people to travel to one city or another (other than distance decay)?How accurately do you believe the gravity model formula predicts actual migratory patterns between places? Explain.

Earnest Ravenstein Earnest Ravenstein (1885)(1885)

1) Most migrants only travel short distances 1) Most migrants only travel short distances to higher populated areasto higher populated areas

2) Migrants created gaps through the flow 2) Migrants created gaps through the flow towards the higher populated areas filling up towards the higher populated areas filling up space between origin and destinationspace between origin and destination

3) Counter-current of migration at destination3) Counter-current of migration at destination 4) Long distance migrants flock towards world 4) Long distance migrants flock towards world

cities or large industrial areascities or large industrial areas 5) The natives of towns are less migratory 5) The natives of towns are less migratory

than those of the rural parts of the countrythan those of the rural parts of the country 6) Females are more migratory than males6) Females are more migratory than males

Until recentlyUntil recently Men, or couples w/o children, young adult or senior Men, or couples w/o children, young adult or senior

citizens, no dependentscitizens, no dependents

Migration IssuesMigration Issues Push factorsPush factors

Things that push people to move away from a locationThings that push people to move away from a location Pull factorsPull factors

Things that draw people to a locationThings that draw people to a location Forced MigrationForced Migration

People forced to leave a given place permanentlyPeople forced to leave a given place permanently Usually based on ethnicity, religion, ideology, etc.Usually based on ethnicity, religion, ideology, etc.

RefugeesRefugees People leaving a location for fear of persecution or deathPeople leaving a location for fear of persecution or death War-torn nations, religious persecutionWar-torn nations, religious persecution Cuban refugeesCuban refugees

Intervening obstaclesIntervening obstacles Things that block migration streamsThings that block migration streams

Intervening opportunitiesIntervening opportunities Things that attract people while in the migration streamThings that attract people while in the migration stream

Cultural HearthsCultural HearthsThe center or starting point of a The center or starting point of a cultural traitcultural trait

Regions can be defined by hearthsRegions can be defined by hearthsExamples?Examples?

Vatican CityVatican CityBirth of Blues (Memphis, Birth of Blues (Memphis, Tennessee)Tennessee)

Cultural DiffusionCultural Diffusion

Relocation diffusionRelocation diffusionHierarchical diffusionHierarchical diffusionContagious diffusionContagious diffusionStimulus diffusionStimulus diffusionExpansion diffusionExpansion diffusion

AcculturationAcculturation The spread of a cultural complex or a cultural The spread of a cultural complex or a cultural

trait from one location to anothertrait from one location to another The process of another culture embracing or The process of another culture embracing or

adding that cultural trait to their cultural complexadding that cultural trait to their cultural complex

AssimilationA culture is completely dominated by another

cultureForced migrationImperialization