Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Limiting the Scope

Spatial data (again, facts about the real world organized by locational coordinates) can be used to describe molecular structures, a human central nervous system, positions of books in a library, or stars in the universe. Since this book relates to geography, we now exclude several categories of spatial data. Usually not considered are data that relate to:

• Conditions that change quickly in time—in matter of hours, days, or even weeks. Current pollution levels, weather, and ties will not be included, although average pollution at a point, climate, and ranges of times could be included. Exceptions to this rule include using sensors to collect immediate data about conditions and put those data out to Internet sites for display on the Web.
• Objects that move about in space—such as automobiles, animals, or people. However, data about flows of these objects past a certain point at a certain time might well be included. Exceptions to this rule include using GPS to keep up with trucks and cars, or to track animals in the wild.
• Circumstances in which the locational identifiers must be more precise than 1 decimeter (a tenth of a meter) to ensure that the related data are useful or valid. The smallest distance separating two adjacent entities that can be distinguished from one another is called the resolution distance, or simply, resolution. If the separation in distance is less than the resolution, the data cannot be used to resolve any differences in the condition or ...