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Once the time to travel across the regions is developed, the only other data
required are the locations of the towns and cities of interest. We used cities and towns from two sources: CIESIN et al. (2004) and the World Gazetteer Database (Helders 2005). ArcView 3.2 was used to calculate the shortest travel time to any point in the specified cities and towns dataset.
Box-and-Whisker Graphs A box-and-whisker graph summarizes a variety of information for a variable in a relatively straightforward diagram. A sample box-and-whisker graph is shown in Figure 2.3. The horizontal lines at the top and bottom of the dia- gram are the “whiskers” and show the minimum and maximum values of the variable. The top and bottom edges of the rectangle, the “box,” show the 75th and 25th percentiles, respectively, of the variable under consideration. The horizontal divider line inside the box represents the median value of the data. These graphs were generated using Stata (StataCorp 2009) with Tukey’s
(1977) formula for setting the upper and lower whisker values, which Stata calls “adjacent values.” Now that we have given a general overview of the models and some of the
data reviewed in this monograph, we are ready to see the results of the models applied to each of the countries studied in the chapters that follow.
FIGURE 2.3 Sample box-and-whisker graph
3.0 3.2 3.4 3.6
2.8 2050 Sources: Authors, using StataCorp (2009) and Tukey (1977).