A need for geo-referenced data within the scientific community has led to the development of comprehensive geographic information systems. Such comprehensive systems are characterized by three fundamental attributes. They possess a data organization which is indexed by using a geographic locator. They have the capability to manipulate and analyze the data base by displaying raw data, to aggregate raw data into classes, to tabulate the distribution of data within a class, and to perform arbitrary arithmetic operations on the data. They also possess the capability to prepare graphical displays of the data in the form of maps. Now that remote sensing has developed as an integral source of data for these data bases, image-based information systems need to have the capability to utilize digital image processing techniques for data entry, and to interface image format data to spatially-referenced tabular data in addition to replicating the computational steps found in the standard comprehensive systems. As the complexity and sophistication of image-based information systems have developed, however, it has become difficult for users, particularly those who do not have digital image processing experience, to fully take advantage of these capabilities. Optimum use of image-based information systems will generally require an experienced user who is familiar with the user response language and syntax, who can anticipate the sequential functions of the system, and who is also familiar with the data base organization and file structure.
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