There is a long tradition in the use of different types of models in transport planning. In multimodal planning spatial models offer great advantages with respect to an explicit treatment of route choice, mode choice, and geographical differences in transport level of service, which in turn can influence destination choice and travel frequencies. In this document we have tried to highlight the different elements in such models and the theories and assumptions behind them. We look into the principals and algorithms in route choice models for auto and transit assignment, theories and principles behind spatial interaction models, discrete choice models, and the traditional four-stage model. The document is concluded with some examples of how one, with limited resources on ad hoc basis, can establish models with one or more stages in common with the four-stage model.