Urban mapping research has demonstrated that historic maps can be integrated with remotely sensed data and related geographic information to successfully detect changing urban land characteristics for large metropolitan areas. Effective and efficient temporal mapping requires that procedures be defined for selecting the temporal range and geographic extent of a study area. Procedures were developed using the Chicago-Milwaukee and Portland-Vancouver metropolitan areas as examples.
Establishing the proper temporal scale requires that one capture the time periods that are critical to characterize the growth experienced in an area. Several factors, including population peaks, significant historical events, and data availability, should be considered together before determining the temporal range and increments for a study.
The geographic extent must not only encompass the areas of significant change but also the landscape that is most threatened by future human impacts. Several factors to consider when defining the geographic limits of a study include growth patterns, development trends, local environmental issues and concerns, data needs of local organizations, and the practical constraints of schedules and resource requirements to map the area defined.
The appropriate selection of temporal and geographic limits is essential to insure efficient mapping and relevance of the database for future studies.
