1. Maddy Walczak & Layla Parsa
GRAVITY MODEL
Maddy Walczak & Layla Parsa

2. WHat is the gravity model?
“The gravity model predicts that the optimal location of a service is directly related to the number of people in the area and inversely related to the distance people must travel to access it.”
-Rubenstein
This model is modified version of Newton’s law of gravitation. It is mainly used to measure the interaction and migration between two cities.

3. Use of the Gravity Model
In the gravity model, interaction is proportional to the multiplication of the two populations divided by the distance between them (distance decay). So, the simplified formula is
(Population of city A)(Population of city B)/Distance^2
If Los Angeles and New York of 1998 are taken into consideration, the formula (in the millions place) would be
(LA: 15.78)(NY: 20.12)/(6) = 52.9
However, if El Paso and Tucson are compared, they would get about an 8. This means that LA and NYC have greater interaction even though they are much farther apart.

4. Picture of gravity model
The shorter the distance between two objects, and the greater the mass of either (or both) objects, the greater the gravitational pull between the objects.