The gravitational formula of the famous physicist Isaac Newton suggests that larger masses are attracted more strongly to each other than smaller ones, while the distance between the two masses reduces this attraction. A so-called gravitational model represents an economic adaption of this physical formula, whereby the attracting forces are interpreted as the mutual attractiveness of economically interacting, spatially separated actors.
Gravitational models imply a relationship between economic activity and geographical distances as well as various other barriers. In economics the masses are often interpreted as gross national products or other relevant variables of the trading partners, the force is originally their volume of trade. This interpretation was first used in the early 1960s. With the help of such models, trade between two countries can be modelled as positive dependent on their cumulative economic performance and as negative dependent on the geographical distance between those two countries.
In the context of a statistical-econometric model (linear regression) the following information is often used for better explanation of trade data: presence of common borders, data on cultural environment (language, geographical areas, common territorial history, etc. ) geopolitical data (free trade area, (civil-)war in the recent past, legal security etc. ), location as landlocked country etc.