Most research involves some type of comparison and contrast to determine differences. Geographical comparison and contrast may be between two or more regions, such as comparing population change in the Sun Belt to the rest of the nation. Often, however, the comparison and contrast is within the same area to determine what changes have occurred since an earlier time. For example, governments, property owners, and insurance companies need to know the historic rate and magnitude of hazardous events such as fires, freezes, and floods; restoration ecologists need to know the ecological characteristics of an area before restoration efforts can take place; and global change scientists need to know what historic land covers were, as well as when, how, and why they changed.
In Philadelphia, land subsidence led to structural house damage, the condemnation, and demolition of more than 1,000 houses, and occasional deaths. The subsidence was related to stream valleys that had been filled with coal ash and cinders that were susceptible to compaction and piping. To locate these historic valleys and determine areas of probable fill, the U.S.Geological Survey used 1890s topographic maps and City of Philadelphia Water Department records to reconstruct the original topography (Chirico and Epstein 2000). GPS control points were used with GIS to correct historic contour data where it was in error. The corrected topographic maps were then compared with the current surface to locate areas of significant surface change. These maps showed where historic valleys had been filled and developed.
Andrea Laliberte and William Ripple (2003) turned to the journals of Lewis and Clark to determine whether humans had an impact upon wildlife populations. They collected information from the journals on nine wildlife species consistently reported as killed or observed for each of the expedition's 506 campsites. Using a GIS they compared the observations to both distance from the nearest settlement or village and density of local settlement pattern. They then summarized the data by ecoregions. Generally, they found that the number of species increased with distance from settlements and as settlement density decreased. Animals were found in greater abundance at the interstices of settlements and villages where possible territorial conflict between groups led to reduced hunting pressures.
Florida citrus, winter vegetable, and sugar cane farmers have inadvertently increased the probability of damaging freezes (Marshall, Pielke, and Steyaert 2003). Throughout the twentieth century, citrus and winter vegetable farmers moved progressively farther south in Florida to escape winter freezes. In 1997, a rare freeze in south Florida damaged crops that were planted on drained wetlands. Land cover from the nineteenth century was used in a meteorological model to determine the weather impacts of draining the wetlands. The model indicated that areas that had been extensively drained and farmed south and southwest of Lake Okeechobee would be colder and that the cold periods would be lengthier than if the wetlands had not been drained.
Geographers at the University of Missouri have been converting U.S. General Land Office survey information to digital form. The survey field notes provide information about land cover before farmers, stockmen, lumbermen, and others instituted massive changes. This information can be used to reconstruct the environment at the cusp of Euro-American settlement. Walter Schroeder and Michael Batek (Batek et al.1999) have used this data to reconstruct vegetation and fire regimes in the Ozarks. Missouri Geographers also combined land survey notes and Lewis and Clark journals to reconstruct vegetation, river channels, and daily weather along the Missouri River corridor at the time of the Lewis and Clark expedition. One of their products is a wonderful animated map (Lewis and Clark Across Missouri).
Geographers at the USGS EROS Data Center are using historic remote sensing and air photos to determine the locations, rates, causes, and consequences of U.S.land cover change (Loveland et al.2002). The national archive of remotely sensed imagery at EROS is now more than 30 years old and has become useful for historic land change studies. This is an example of a traditional geospatial data set that has grown in value with time because the imagery from the 1970s and 1980s is now old enough to be useful in detecting significant changes to the nation's land surface, and advances in Geographical Information Sciences provide tools to look at the data in new, more relevant ways.
Old data, often from nontraditional sources, may become valuable 'new'
data with increased relevance and usability when coupled with geospatial
technologies and basic geographical ideas and principles. For example
the notions of distance decay and settlement patterns provided new insights
from Lewis and Clark's mammal records. The research showed that both
small, frontier settlers and Native Americans had an impact upon animal
populations.
The answers to many of today's significant questions often depend upon
a knowledge of how humans and natural cycles have altered the earth's surface.
Often these questions cannot be answered without historic information that
may be available only from nontraditional sources. The data from
these sources was often irrelevant or unusable before the development of
the tools of Geographical Information Sciences.
Citations
Batek, Michael J., Alan J.Rebertus, Walter A.Schroeder, Timothy L.Haithcoad, Eric Compas, and Richard P.Guyette. 1999. Reconstruction of Early Nineteenth-century Vegetation and Fire Regimes in the Missouri Ozarks. Journal of Biogeography 25. Chirico, Peter G.and Jack B.Epstein. 2000. Geographic Information System Analysis of Topographic Change in Philadelphia, Pennsylvania, During the Last Century. U.S.Geological Survey Open File Report 00-224. Laliberte, Andrea S.and William J.Ripple. 2003. Wildlife Encounters by Lewis and Clark: A Spatial Analyis of Interactions between Native Americans and Wildlife. BioScience 53(10):994-1003. Lewis and Clark Across Missouri (http://lewisclark.geog.missouri.edu/index.shtml) Loveland, T.R., T.L.Sohl, S.V.Stehman, A.L.Gallant, K.L.Sayler, and D.E.Napton. 2002. A Strategy for Estimating the Rates of Recent United States Land-Cover Changes. Photogrammetric Engineering & Remote Sensing. October: 1091-1099. Marshall, Curtis H., Roger A.Pielke sr., and Louis T.Steyaert. 2003. Crop Freezes and Land-Use Change in Florida. Nature 426 (6 Nov.2003):29-30.