BOX 8.5
Illustrative Difficulties That Teachers and Students Confront When Working with GIS

Four examples illustrate situations in which teachers and/or students encounter problems while working with ArcView software. Each example is keyed to a particular part of the software. A brief explanation of what goes wrong and why is presented, followed by a suggestion on how the problem has been or can be remedied.

1. On or Off Themes. ArcView 3 uses a “View” frame composed of a map space and a “Table of Contents” (TOC). Layers of data, known as themes in ArcView, are either on (and accessible) or off, according to a checkbox in the TOC. Newly added themes are not turned on automatically. Novice users will often wonder what they did wrong or why something fails to work, when all they have to do is turn on the data layer. Figure 8.11 shows the result of adding a theme in ArcView 3. It appears atop the TOC but is not turned on by default. For adults, this sometimes means that they will re-add the theme several times before saying, “Oh, I need to turn it on … duh!” with which students do not have nearly as much trouble. This problem is remedied in ArcView 8, which automatically turns on added features.

2. Active and Inactive Themes. In its mapping space, ArcView 3 relies on a concept of “active theme” (i.e., a data layer against which a process is to be accomplished). The active theme is established by clicking one time anywhere on the name or symbols of that data set within the TOC; an active theme looks somewhat raised or embossed. Novice users attempt to run a process without remembering to specify the active theme. When an unexpected result occurs, users are often baffled until they are reminded by more experienced users to check which theme is active. Figures 8.11, 8.12, and 8.13 show the condition of having 0, 1, or 2 specific themes active. Notice that many buttons and tools are grayed out when there is no active theme, because a process cannot be applied to nothing. ArcView 8 resolves this problem by introducing “right-click” operations, which require users first to identify a theme and then to choose an activity. Figures 8.12 and 8.13 show ArcView 3 after the user has made one theme (Figure 8.12) or two themes (Figure 8.13) active by clicking on their names.

FIGURE 8.11 On or off themes: adding a theme in ArcView 3. The “Highway” theme has been added but is not turned on. No themes are active in this display.

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