Huff model

The Huff model estimates the probability that a person will visit a particular location rather than a competing one. It weighs two things against each other: how attractive each destination is, usually by size, and how far away it is. Attractiveness pulls, distance pushes, and the model turns that into a share for each destination.

This makes it the accessibility method for competitive situations. Where 2SFCA asks whether capacity is sufficient, the Huff model asks where people will actually go, which is the question in retail site selection, and in any planning case where several facilities of the same kind compete for the same population. It also gives an estimated catchment that overlaps with its neighbours, which matches reality better than drawing hard boundaries.

Two parameters decide the outcome. The measure of attractiveness, often floorspace or capacity but sometimes something better if you have it. And the distance decay, which sets how quickly willingness to travel falls off. Both are choices, and both should be stated alongside the result.