A Basis for Understanding
It is no secret that many of the world's archaeological and cultural treasures -- the Egyptian pyramids and Britain's Stonehenge certainly come to mind -- are slowly falling victim to the ravages of pollution and the elements. But that, unfortunately, is only part of the story. Many important archaeological sites lie beneath the soil, hidden from view. Some of these sites have been damaged by agriculture and mining. Still others have been destroyed, leaving irreversible holes in the archaeological landscape. The archaeologist tries to detect, document and map these sites, aiming to protect them or, at the very least, extract as much information as possible before they are lost forever.
It is understandable that archaeologists today seek an easy means to end the laborious tasks that they endure each and every day in their search to uncover clues about the past. For much of recent times, these same scientists have endured maps that are either inaccurate, not to a scale that fits their needs, or are so completely deficient of data that meets even the lowest of standards, that it is often impossible to record human events. Thanks to the advent of computer technologies, however, those arduous days are quickly becoming a thing of the past themselves.
More specifically, with the rapid advance of geographic information systems (sciences, so some say), archaeology has finally come face to face with its counterpart – geography. Indeed, both fields are spatial; they both deal specifically with human interactions with their environments, whether past or present. Geography may have been in the forefront to accept either aerial photography or satellite imagery as a way to visualize our world, but it may soon be the field of archaeology that overtakes its counterpart in the use of these applications for understanding just how important these “techniques” are to both past and present cultural interactions – a field that geography is most interested to this very day. While many scholars continue to debate the academics of human geography versus geographic technology, the field of archaeology is beginning to comprehend that both are of the utmost importance; both are not just related, they actually rely upon each other to achieve the best insight of the problem at hand.
For example, since the days of Heinrich Schliemann's search for ancient Troy, archaeologists have been confronted with the problem of how to record and analyze the spatial characteristics of archaeological data. When researchers wanted to analyze this information, they were required to spend much of their time transposing it to new paper maps. Today, this time-consuming process is nearing its end as researchers move to take advantage of computers and the geographic information systems (GIS) that they offer.
“The one area where archaeologists have generally used GIS, and one of the most important issues and uses for GIS in current archaeological research, is in predictive modeling of site locations and in the environmental modeling of landscapes”.  In recent years, the use of GIS has experienced rapid growth, and archaeology has been just one of the many disciplines that have been caught up in this technological whirlwind, reflecting the importance of space, spatial concepts, and spatial modeling. Archaeologists, as researchers and resource managers, understand that geographic variables exert a strong influence on human behavior today. Moreover, they are also keenly aware of the significance of theses influences in the past. Geographic analysis and modeling, through the use of geographic information systems, provides answers to a variety of questions helping researchers make informed decisions.
Although archaeology has been deeply involved with GIS and remote sensing technologies for some time, it has been only over the past 10 or 15 years that they have risen to prominence as analytical tools. In great part, this sudden increase of interest has been stimulated by advances in technology, including the widespread availability of GPS, the development of imaging systems with extraordinarily high spatial resolution, the continued improvement of GIS software, and the appearance of personal computers capable of performing sophisticated analyses of GIS and remotely sensed data.
Changes in policy, however, have also been important. The U.S. government only recently (in 2000) turned off selective availability for civilian GPS users, making it possible for them to locate sites and make maps using store-bought satellite receivers with a high level of accuracy. Additionally, governments have also made available previously classified air photos and satellite imagery. Together, these changes have provided archaeologists with important tools useful in the spatial analysis of archaeological phenomena.
For example, many projects now use satellite imagery to generate data about landforms and vegetation cover, which are then used to create data layers directly in a GIS. Such imagery is also used to build digital elevation models (DEM) of project areas that, in combination with data derived from archaeological surveys, can be used to evaluate ancient trade routes, patterns in locational preference, and political boundaries. Even more exciting is the use of GIS in combination with near-surface sensed data (such as that derived from a ground-penetrating radar) to look below the surface of the ground at an archaeological site before excavation takes place. Not only can archaeologists visualize their sites in new ways, they also have the powerful analytical capabilities of GIS at their disposal that can be used to explore these data. 
Archaeology routinely deals with an enormous amount of spatial data, varying in scale from the relative locations of archaeological sites down to the positions of individual artifacts. In the late 1970s, the method of storing archaeological data began to slowly change from paper to digital. As access to affordable computers became more common, archaeologists could see the advantages of digitally storing their spatial data for analysis. During this era, several commercial vendors began to develop primitive GIS systems in an attempt to meet the needs of researchers.
A GIS is best thought of as a dynamic database for spatial data -- one that provides tools that can help integrate a variety of data sources, maintain and manage inventories, visualize data using dynamic maps, and perform modeling and analysis. Archaeological researchers routinely have to deal with large amounts of data acquired through numerous sources, and most often of varying type. Chevallier, for example, in his quest for examining ancient Roman roads, searched through thousands of pages of Latin text, along with medieval maps and illustrations.  GIS software packages provide archaeologists with almost unlimited ways to manage, analyze, and research these various types of cultural resources (Figure 1). Indeed, the power and beauty of GIS lies in its ability to link various objects on a map to a database, thereby combining the graphical display of data with database query and analysis functionality.
Once a GIS layer is built, the spatial relationships between mapped features can be analyzed for patterns that would not be readily apparent if the database was viewed in tabular format. Using GIS, archaeologists can analyze geographic data within a single layer, such as a site distribution map, or the relationship between multiple layers in an effort to examine how environmental variables such as topography, soil type, or distance to water affect site location.
GIS and remote sensing technologies can be especially useful in locating and documenting those archaeological sites that are still hidden from view. Tragically, such sites are increasingly threatened with destruction. “The main threat is erosion, accelerated in areas with intensive agriculture, which is removing the archaeological layers centimeter by centimeter.”  Mining, along with the construction of roads, railroads, and industrial areas is also taking its toll. The loss of such sites leaves a gap in our shared archaeological heritage. Therefore, we must act now to detect and document sites before they are gone.
And what a wealth of information can be found. Much of human history can be traced through how humans have interacted with and changed their surrounding environment. The use of GIS and remote sensing technologies offer the archaeologist the opportunity to detect these effects – effects that are often invisible to the naked eye. This information can then be used to address issues involving human settlement patterns, environmental interactions, and even possible climatic changes.
Archaeologists are interested in finding out how ancient people adapted to their environment and what factors, if any, may have led to their collapse. Once these data have been collected, archaeologists may then be able to apply this information to modern societies so these mistakes can possibly be avoided. Understanding how ancient man managed Earth is important for the success of current and future societies. 
One of the foremost applications to make its way into the mainstream of archaeology was the use of aerial photography. Archaeologists have been using this remote sensing technique since just after World War I as a way to locate buried structure, roads, and other features of ancient landscapes. Early pilots noticed strange circles and square patterns from the air that were not visible on the ground -- patterns that were not part of the modern landscape. They found that these were actually archaeological sites, ancient roads, or other features of buried ancient societies. These early pioneers conducted the first such surveys in Europe and the Middle East during the 1920s. Charles Lindbergh conducted similar surveys in the Western United States in 1929 (Chaco Canyon), as well as in Central America in the 1930s.  Additionally, aerial photography played an extensive role in located long since abandoned roads of the Inca Empire and, according to Hyslop, will “become more significant as (these) road networks become better known”. 
Since the computer can be programmed to look for distinctive "signatures" of a known site or feature in areas where surveys have not been conducted, remote sensing can be quite the discovery technique. Such signatures serve as recognition features or fingerprints; characteristics such as elevation, distance from water, distance between sites or cities, corridors, and transportation routes can help to predict the location of potential archeological sites. 
It has only been since the late 1980s that GIS has truly gained popularity in archaeology. Since 1988 there has been rapid growth in the application of GIS techniques as a tool both for archaeological research and for cultural resource management (CRM). Within the research community, many computer-literate archaeologists have applied GIS to their field of interest, be it environmental archaeology, regional settlement studies or intra-site spatial analysis, as a logical extension to the use of special-purpose mapping or spatial analysis programs. More than a few have made it their special domain and are exploring both the theoretical and methodological implications of this new technological integration. 
Geographic information systems give the archaeologist yet another tool to aid in linking archaeological method with theory.  The result is that GIS is finally taking its due place alongside databases, word processors, and desktop publishing systems and can be used on a daily basis by many archaeologists. “Geographic Information System technology, and the integrally related mapping and remote sensing technologies, that is based on computer processed, spatially related data files, are now being used by thousands of organizations”. Along with the rapidly increasing availability of the systems themselves, there is also a growing body of literature devoted to GIS, either in specialist journals devoted to the technology or in case studies of archaeological applications. Much has already been learned about this integration of science and technology and trends such as these will continue with even more fervor into the foreseeable future. 
Allen, K.M., Green, S.W., and Zubrow, E.B.W. (Eds), 1990, Interpreting Space: GIS and Archaeology, London: Taylor & Francis
Brose, David and N’omi Greber, 1979, Hopewell Archaeology: The Chillicothe Conference, Kent, OH: The Kent State University Press
Chevallier, Raymond, 1976, Roman Roads, Berkley, CA: University of California Press
Hyslop, John, 1984, The Inka Road System, Orlando, FL: Academic Press
Johnson, A. I., Pettersson, C. B., and J. L. Fulton (Eds), 1992, Geographic Information Systems (GIS) and Mapping – Practices and Standards, Philadelphia, PA: American Society for Testing and Materials
Lock, Gary and Zoran Stančič (Eds), 1995, Archaeology and Geographical Information Systems, London: Taylor & Francis
Maschner, Herbert D.G. (Ed), 1996, New Methods, Old Problems: Geographic Information Systems in Modern Archaeological Research, Carbondale, IL: Center for Archaeological Investigations
Westcott, Konnie L. and R. Joe Brandon (Eds), 2000, Practical Applications of GIS for Archaeologists: A Predictive Modeling Toolkit, London: Taylor & Francis
Wheatley, David and Mark Gillings, 2002, Spatial Technology and Archaeology: The Archaeological Applications of GIS, London: Taylor & Francis
 Maschner, Herbert D.G. (Ed), 1996, New Methods, Old Problems: Geographic Information Systems in Modern Archaeological Research, pp 10, Carbondale, IL: Center for Archaeological Investigations
 Chevallier, Raymond, 1976, Roman Roads, Berkley, CA: University of California Press
 Nials, Fred, et al., 1987, Chacoan Roads in the Southern Periphery: Results of Phase II of the BLM Chaco Roads Project, Bureau of Land Management, Santa Fe, New Mexico
 Hyslop, John, 1984, The Inka Road System, pp 335, Orlando, FL: Academic Press
 Maschner, Herbert D.G. (Ed), 1996, New Methods, Old Problems: Geographic Information Systems in Modern Archaeological Research, pp 25, Carbondale, IL: Center for Archaeological Investigations
 Johnson, A. I., Pettersson, C. B., and J. L. Fulton (Eds), 1992, Geographic Information Systems (GIS) and Mapping – Practices and Standards, pp 1, Philadelphia, PA: American Society for Testing and Materials
 Allen, K.M., Green, S.W. and Zubrow, E.B.W. (Eds), 1990, Interpreting Space: GIS and Archaeology, London: Taylor & Francis