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Los Angeles Ethnicity: Labeling standard deviational ellipses
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The labels in this example are parallel to the major axis of the ellipse and when possible centered within the minor axis of the ellipse.
The labels in this example are parallel to the major axis of the ellipse and, when possible, centered on the minor axis of the ellipse.

What: The labels for the standard deviational ellipses are aligned within the ellipses and are colored using the same hue as the ellipse, though with a much lower value so that the labels are darker and easier to read. The labels identify the ethnic group it represents, how many people are in it, and over how large an area are they spread.

Why: When evaluating standard deviational ellipses, it is important to understand and be able to compare the ellipse sizes, location, orientation, ratio of the major and minor axes, and counts. Adding a label with some of that information makes it easier for the map reader to make comparisons among the ellipses.

How: The labels were placed using the Maplex Label Engine. The labels use a custom label expression. Here is how we set up our labels, starting with the label expression and finishing with the label placement:

  1. First we created the label expression:
    1. Open the Label Manager using the first button on the Labeling toolbar. On the left, select the label class for the layer with the standard deviational ellipses.
    2. We used the following string, which concatenates hard coded strings like "Asian: " and "Area " with values from fields like [Poprepd] (our population field) and [Area_SqMi]. It also uses a function that contains programming logic, like VbCrLf which is a Visual Basic (VB) function to add a new line (Cr is carriage return and Lf is Line feed):
    3. "Asian: " & " " & + [PopRepd] & " persons" & VbCrLf & "Area = " & [Area_SqMi] & " Sq. Miles"

  2. Next we set the label placement properties. To do this, we used all the defaults for the Maplex Label Engine with the exception of these two changes:
    • Position: Straight
    • Stack label: unchecked because our custom label expression already has stacking using VbCrLf.

The result is that labels are, when possible, centered within the polygon. For ellipses, this means the labels are centered on the main axis. When conflicts arise, the Maplex Label Engine places the label within the ellipse but does not change the angle, which is ideal in this case.

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