FIGURE 2.1 A space-time path.

Capability constraints limit an individual’s participation in events in space and time by requiring that paths be in certain locations for fixed time intervals and by determining the steepness of the path when traveling outside those intervals. For example, capability constraints might lead one to devote a large amount time to physiological necessities such as sleeping, eating, and personal care, and these usually can occur at a limited number of locations, but transportation technologies could facilitate mobility from one of those locations.

Coupling constraints refer to the need to coordinate—to coincide in both space and time with other persons—in order to produce, consume, and participate in social activities. A job may require presence at a work site for a fixed number of hours per week. However, stores, medical facilities, and government offices are at limited numbers of locations in space and are open at limited hours.

Authority constraints are legal, economic, and social barriers that restrict the ability to be in particular locations at certain times. Gated suburban communities illustrate the attempt to impose authority constraints on nonresidents. The growth of spatial data in digital form and



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