Geographic Information Systems: An Introduction, 3rd Edition

8.3 Communications Between Users and Computers

Users and computers communicate at the human–machine interface (MMI). The features of MMI are vital in GIS applications, where users need to control communications with their computers by deciding what is to be done at what time and in what order—always with the option of canceling an action midway through a communication.

In particular, MMI communications require input/output devices, such as ordinary keyboards, special function keys, mice, joysticks, and so on, along with their supporting software. Tablets are also used in interactive human–machine communications. A tablet is a graphical input device in which positions can be selected by using crosshairs instead of pointing on screen.

The dialogue between a user and a computer is interactive when user commands result in immediate system responses in the form of messages, error messages, new choices, and so on. On-screen dialogue may be controlled by:

• User commands to the system
• User responses to system messages or queries
• Menus of options that elicit user input
• Icons (pictorial symbols used in menus) to which the user points the cursor

Commands

The first software systems were controlled by relatively cumbersome sets of commands and had no interactive features. Many GISs contain remnants of these earlier complexities, although choices between commands and menus are often available. To use commands, users must enter relatively long instructions, which in turn require a knowledge of ...