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

Exploring Basic GIS Data Storage Models

As you know, large amounts of computer data are usually stored on devices called disk drives. They are usually mechanical, with a motor spinning a disk with a magnetic coating, but they can also be completely electronic – as in flash or thumb drives. Disk drives constitute the “slow memory” of a computer. It takes a computer thousands of times longer to retrieve data from slow memory than from fast memory. An analogy with human processes might be that, in your brain—where you remember your friend’s names, your home telephone number, or the route you drive to work—is located your “fast memory” or your “electronic memory.” On the other hand, the name of your uncle’s second cousin, the phone number of the dry cleaner, or how to navigate to Punxsutawney, Pennsylvania, are things that you probably have to look up; they reside in slow memory—family documents, telephone book, and road map (or a GIS).

Most of the data that exists in the world on computers is, of course, not in use (not being printed, analyzed, or otherwise processed) at any given moment and, therefore, is not contained in the “fast” electronic memory of a computer. Data sets in the slow memory of a computer are, in their most basic form, just sequences of 0s and 1s. However, beyond that, well beyond that, such data sets are organized by storage paradigms. You are familiar with the idea of folders on a disk drive. Each folder can contain files and other folders. The operating system ...