observed that spatial interaction is effectively controlled by three flow-determing factors that he called:
the actual or potential relationship of two places or regions that each produce different goods or services for which the other has an effective demand, resulting in an exchange between the locales
Acceptable costs of a spatial exchange; the cost of moving a commodity relative to the ability of the commodity to bear that cost
Is a function of three interrelated conditions:
the characteristics and value of the product
the distance, measured in time and money penalties, over which it must be moved
the ability of the commodity to bear the costs of movement
the concept that closer opportunities will materially reduce the attractiveness of interaction with more distant--even slightly better--alternatives; a closer alternative source of supply between a demand point and the original source of supply
Friction of distance
a measure of the retarding or restricting effect of distance on spatial interaction.
Generally the greater the distance, the great the "friction" an the less the interaction or exchange, or the greater the cost of achieving the exchange.