This paper argues that existing models of urban concentrations are incomplete unless grounded in the most fundamental aspect of proximity; face-to-face contact. Face-to-face contact has four main features; it is an efficient communication technology; it can help solve incentive problems; it can...

While transport costs have fallen, the empirical evidence also points at rising total trade costs. In a model of industry location with endogenous transaction costs, we show how and under which conditions a decline in transport costs can lead to an increase in the total cost of trade.