Pilgrim B. (1969) Choice of house in a new town, Reg. Studies 3, 325–330. A computer simulation of housing, industry and population growth has been built by the Local Government Operational Research Unit for three of the Scottish new towns. This is a planning decision model which can be used for producing population forecasts and for testing various policies on house building, rent structures and employment growth. One part of the simulation is a mathematical description of how households are allocated houses. This is based on a gravity model approach. The paper describes how this was developed and to what uses it can be put.