FIGURE 3 The classes option for ExploreMap. Any subset of classes can be selected by clicking on the legend boxes in this case, classes and 4 are shown. without reservation subjects used Classes not only to identify the location of individual classes, but also to examine patterns and trends. Although useful, the Classes option is constrained by how the da classed (in Figure 22.3, a five-class optimal map is used). One solution to this constraint is the Reclass function, which permits changing the method and number of classes. An option within Reclass, Compare Maps, permits presenting up four maps simultane- ously (each map can have a different method of classi fication or number classes). For example, Color Plate 14 compares four methods of classification for ass maps: equal intervals, quantiles, optimal based on the mean, and optimal based on the median alternative to reclassing the data is the subset option, which permits focusing on an arbitrary range of data. To assist users in selecting data to focus on, ExploreMap provides a dispersion graph (Color Plate 22.1A) illustrating the distribution of an attribute along the number line; the current class breaks, and standard deviation can be shown on the dispersion graph (only the median is shown in Color Plate 22.1A) Users can simply click a desired range (or type a range of values), and the specified range is drawn in a highlighted color (blue used in Color Plate 22.1B display all values less than the median) Although subset enables users to highlight selecte portions of a data set, it is limited because a highlighte data are shown in a single color, and because real-time interaction with the dispersion graph is not possible more flexible approach would permit a range of shades for the highlighted color (say, a range of instead a constant blue). This would enable users to focus on subset of the seeing the variation wit that subset. A more flexible approach would also allow