【導讀】student.(suchasbiology,botany,forestry,andgeology);theEarth.entireglobe.

　　

【正文】 on output from a GIS. In interacting with a geographic information system, the user must not only understand the application, but also the characteristics of the tool and the system itself. Like all advanced technologies, the kinds of spatial data processing systems we will discuss must be employed wisely, to keep us from fooling ourselves. The following chapters discuss the wise use of geographic information systems. 9 Chapter 2 Background and History Geographic information systems evolved as a means of assembling and analyzing diverse spatial data. Many systems have been developed, for landuse planning and naturalresource management at the urban, regional, state, and national levels of government agencies. Most systems rely on data from existing maps, or on data that can be mapped readily (Shelton and Estes, 1979). The development of geographic information systems has its roots in at least two overlapping areas: an interest in managing the urban environment (particularly in terms of planning and renewal), and a concern for the balancing peting uses of environmental resources. Technology has played a critical role in addressing these concerns. If we look at John Naisbitt39。s 1984 work Megatrends, we can see why. Megatrends discusses new directions which are transforming our lives. In Naisbitt39。s words, none of the megatrends discussed “is more subtle, yet more explosive than . . . the megashift from an industrial to an information society.” This information society had its beginnings in 1956 and 1957. Indeed, the advances in munications and puter technology that facilitated the widespread dissemination of the ideas and concepts contained in Rachel Carson39。s book Silent Spring also provided the foundations and requirements that necessitated the construction of automated geographic information systems. Today, environmental scientists and resource managers have access to more data than ever. Naisbitt (1984) estimates that scientific information is doubling every five years. The key to coping with this information explosion is the employment of systems systems that will take the data, analyze it, store it, and then present it in forms that are useful. These are the requirements of an information system. The Cartographic Process According to Robinson and Sale (1969), cartography is often described as a meeting place of science and art. This science/art is fundamentally directed at municating information to a user and is central to an understanding of the strengths and weaknesses of geographic information systems technology. Much of the material contained in this book is directly related to essential elements of the cartographic process, which involves a body of theory and practice that is mon to all maps. Maps are both a very important form of input to a geographic information system, as well as mon means to portray the results of an analysis from a GIS. Like a GIS, maps are concerned with two fundamental aspects of reality: locations, and attributes at locations. Location represents the position of a point in 10 twodimensional space. Attributes at a location are some measure of a qualitative or quantitative characteristic, such as land cover, ownership, or precipitation. From these fundamental properties a variety of topologic and metric properties of relationships may be identified, including distance, direction, connectivity and proximity. As Robinson et al. (1984) observe, “a map is therefore a very powerful tool”. Indeed, maps are powerful tools for municating spatial relationships. Following Robinson et al., maps: ? are typically reductions which are smaller than the areas they portray. As such, each map must have a defined relationship between what exists in the area being represented, and the mapped representation. This relationship is of primary importance. Scale sets limits on both the type and manner of information that can be portrayed on a map. ? involve transformations. Often in mapping, we are faced with a need to transform a surface which is not flat (such as a portion of the earth39。s surface). In order to represent such a surface on a flat plane, map projections are employed (see section ). Choice of a particular projection has an impact on how a given map may be used. Plane coordinate grids are often used on maps as systems of reference. ? are abstractions of reality. Maps are the cartographer39。s representation of an area, and as such, display the data that the cartographer has selected for a specific use. Thus, the information portrayed on a map has been classified and simplified to improve the user39。s ability to work with the map. ? contain symbols which represent elements of reality. Few map symbols have universally accepted meanings, but some maps use a standardized set of symbols. ? portray data using a variety of marks, including lines, dots, tones, colors, textures, and patterns. In addition to these basic characteristics of maps, the user of maps and other products of a geographic information system should understand the errors which may affect them. The sources of errors fall into three categories (Burrough, 1986): obvious sources, those resulting from natural variation and original measurement, and those arising through processing. Obvious sources: The source data may be too old to be of value. The areal coverage of a given data type, within a given time frame, may not be plete. 11 The scale of the map may restrict the type, quantity, and quality of the data which may be presented. The number of observations within the target area may not be sufficient to be able to determine the spatial patterns in the objects of interest. Practical matters such as the time, funds, and staff which are