.., data = iris, color = Species)</a></code>, the <code>Species</code> variable is used to determine how to color the points.  Here, <code>Species</code> is "mapped" to the <code>color</code> attribute.  Both continuous and categorical variables can be mapped.  In the case of continuous variables, the range is cut into slices and attributes are applied to each interval.  The mapping from the values of the variable to the actual plot attributes is determined based on the theme.</p>
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