Time-space convergence is a measure of change in the effort required to overcome distance. Generally, it is defined as the average rate of decline in travel time between two places over time. For example, owing to innovations that span the eras of stagecoach travel to automobiles on limited-access highways, Boston and New York have approached each other at an average annual rate of 22 min per year between the years 1800 and 2000. The parallel concept of time-space divergence provides for the tangible measurement of increases in separation between places that result from traffic congestion and failure to maintain infrastructure. Implicit in the convergence}divergence viewpoint is the recognition that physical points (places on the earth) are in relative motion with respect to one another whenever functional measures (such as traveltime and cost) are used as the distance metric. Because levels of investment in transportation and communication technologies are not uniform, some places converge much more rapidly with the remainder of the settlement system than others. Some places, bypassed by modern space-adjusting technologies, will diverge, and others will converge and diverge selectively relative to various parts of the urban system. Variations in the set of rates that define convergence among all possible pairs of places create a nonhomogeneousmtime-space that is relative and dependent on the inferred movement of places with respect to one another. In this time±space, places are seen to compete in their quest to gain relative accessibility over other places, thereby gaining advantages for attracting
economic and other opportunities.