Urban Dynamics: Temporal Mapping

Urban Sprawl

The problems society faces due to the growth of cities and the concentrating of human populations into large metropolitan regions are just beginning to be fully recognized as a significant global problem. In his MacArthur Award lecture, Peter M. Vitousek (1994) states that

"Three of the well-documented global changes are increasing concentrations of carbon dioxide in the atmosphere; alterations in the biochemistry of the global nitrogen cycle; and on-going land use/land cover change".

Urban growth rates show no signs of slowing especially when viewed at the global scale. Cities have gone from small isolated population centers to large connected economic, physical, and environmental features of our planet.

Most major metropolitan areas face the growing problems of urban sprawl, which include a loss of natural vegetation and open spaces and a general decline in the spatial extent and connectivity of wetlands, wildlife habitat, and agricultural lands. Residential and commercial development is replacing undeveloped land at an unprecedented rate.

Rate of Change

These land use/land cover changes can be immense but are difficult to grasp when they occur incrementally. Recently, the data from Earth resource monitoring satellites has dramatically illustrated the rates at which these human-induced changes are occurring nationwide. Illustration of Change

Changes to the Landscape

The San Francisco/Sacramento and Baltimore/Washington temporal mapping projects have successfully demonstrated the utility of integrating existing historic maps with remotely sensed data and related geographic information to dynamically map urban land characteristics for large metropolitan areas. These regional databases provide a strong visual portrayal of recognized growth patterns, and dramatically convey how the progress of modern urbanization results in profound changes to the landscape.

Both the San Francisco Bay and the Baltimore-Washington datasets (165 Kbytes) document the dramatic increase in urban development following World War II and continuing to the present day. Each urban database focuses attention on the forces influencing the creation of the spatial patterns and corridors that have developed over time. The principal transportation data layer clearly demonstrates the influence that the transportation infrastructure (roads, railroads, and seaports) has exerted on population development. The hydrography data layer contributes to historical understanding by depicting the loss of navigable rivers by siltation, the development of reservoirs for water supplies, and the changing shoreline resulting from harbor development and salt pond formation.

Environmental Impacts

Urbanization exerts heavy social, ecological, environmental and climatic pressures on surrounding lands in comparison to its spatial extent. It is imperative that we understand the determinants of land use (demographics, technology, levels of affluence, etc.) so that future patterns of land use and land cover can be projected, planned, and managed under sustainable conditions.

The Role of a Temporal Database

The original impetus for building a temporal database of urban extent can be traced to five simple ideas.

• Urbanization is an important component of global change research which is not being addressed by any of the national research agendas.
• Historical data on urban extent can be used to calibrate a cellular model in order to predict regional patterns of urbanization.
• USGS topographic maps can be used to derive the extent of urban and built-up areas for the last 100 years.
• Landsat data can be used to map development from 1972 to the present.
• A time-series animation can be used to better convey the dramatic land use changes resulting from urbanization.

This project demonstrates an advancement in the technology that can be applied to the study of spatial temporal dynamics related to human impacts on land transformation. This knowledge-base and technology must be strengthened to meet the goals of national programs such as NASA's Mission to Planet Earth (MTPE), the Global Change Research Program, environmental assessment and the growing interest in developing methods for sustainable development. This project has many facets, in particular, it provides a temporal dimension to the current USGS land use and land cover mapping activities. The project offers many additional opportunities, including a natural testbed for the national framework concepts in data integration and metadata specifications.

The Future

Temporal urban databases have immediate applications in monitoring urban sprawl, watershed analysis, environmental assessment, analyzing patterns of sedimentation, hydrologic modeling, sustainable development studies, land surface degradation, surface temperature modeling and developing predictive modeling techniques to better forecast future areas of urban growth.

Public reaction to this experimental mapping work has been very positive and supportive of this innovative use of a temporal GIS database. The interest generated by applying modern mapping techniques to regional problems enhances community support and should be used to build a broader temporal mapping program of national and global urbanization phenomena.