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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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User Selection of Classes
____ 8. Notice each vertical blue line. The value at its top end indicates the break value as well. So, the first category consists of 23 values, 19 of which are at the lower end (look at the height of the column), and 4 of which are toward the upper end of the category. The range of this category is from 1003 to 5809.
____ 9. Use the mouse cursor to drag one of the lines. Notice that the Classification Method has changed to Manual—the method selected when the software realizes that you are going to be in charge of where the class breaks are. By moving the lines around, you can choose the Break Values (look in the pane to the right). Also observe, as you move a break line, that the number of values in the class to the left of the break line is dynamically displayed at the bottom of the window. Set the break values—the value at the high end of each category—between classes to approximately 2000, 6000, 11000, 16000, 26000. By doing this, you see that you are putting each natural group of values in a class by itself. Click OK. In the Layer Properties window, click Apply, then OK.
____ 10. Examine the T/C. The five categories into which you have put the populations of FEMALES are represented by increasingly darker colors of green. Note that the range of each class is shown next to its symbol. Look at the map. Notice how much easier it is to see the clusters of similar values.
____ 11. In Layer Properties, click Classify again. By highlighting and typing ...

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