Deriving the Gravity Equation To derive the gravity equation, we assume each country
produces a differentiated product to apply the monopolistic competition model. With a
differentiated product, the import demand for goods produced by Country 1 depends on
(1) the relative size of the importing country and (2) the distance between the two
countries. The relative size of the importing country (Country 2) is measured by its GDP,
as compared with the rest of the world (Share2 = GDP2/GDPW). The distance between the
two countries provides a measure for the transportation costs associated with exporting
the good from one country to another. Raising to the distance between Country 1 and
Country 2 power, or distn, we have that the exports from the former to the latter are equal
to the following equation:
APPLICATION
The Gravity Equation for Canada and the United States
The gravity equation may be applied between countries, provinces, or even states of a