Two contradictory forces are playing in the dynamics of the poles (or clusters):
- Centripetal forces. Are the outcome of factors promoting the efficiency and competitiveness of economic activities and therefore incite the attractiveness of a pole. They include market size (economies of scale), the availability of labor, and many external economies linked with agglomeration (similar inputs and/or outputs).
- Centrifugal forces. Are the outcome of many factors such as high prices and congestion, which may undermine the competitiveness of some activities and incite economic activities to seek alternatives elsewhere. Since several factors of production such as land and natural resources are immobile, it may incite a relocation as they become scarce. This is particularly the case for land as resources can be transported.
Transportation is an important factor in this process as it concomitantly supports centrifugal and centripetal forces. Transportation could be a centripetal force favoring the convergence of activities in a cluster because of the accessibility this cluster can have to a broader distribution system. This is particularly the case when a cluster has an intermodal facility such as a port, an intermodal rail terminal, or an airport. Transportation could also be a centrifugal force if savings compensate the supplementary costs imposed by longer distances from major markets in production factors (labor, land, taxes, etc.) and access to new resources. Under such circumstances, transportation can incite relocation away from an existing cluster.