Exploiting the theory of a classic gravity model, the Market Accessibility index is a measure of potential economic connectivity between village/towns and big cities. These population centers are considered a proxy of market size or population potential. This metric discounts the market size proxy by an estimate
of travel time along a transportation network, which assigns little relevance of a market size in a very far place from the origin or, conversely, assigns a strong relevance for markets in close proximity to the origin. Using the transportation network and estimated travel time is a more realistic measure of
economic distance than Euclidean distance because not all distances are equal in travel time and physical or man-made barriers may provide routes that are not straight line distance. Since various methodologies exist for the discount of the market size, a robustness test is suggested.