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Area graph
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Area graphs show trends in values, just
as line graphs do. Drawn in their default style (stacked, as
in this example), area graphs also show the relation of parts
to the whole and to each other.
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The area graph consists of one or more lines drawn on an X-Y grid, with the
area between the line and the X axis filled in. Like
line graphs, area graphs show trends in
values. With their solid look, area graphs convey quantities with somewhat more
emphasis--and the trends themselves with somewhat less emphasis--than line
graphs do.
Drawn in their default style (stacked, with each data set layered on top of the
previous one), area graphs also allow a comparison between parts or between one
part and the whole.
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Area graphs are available in three forms: stacked, absolute, and stacked
percentage. See the example above and the ones on the next page.
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The X axis always represents the independent variable, which is most often a
time scale. The Y axis shows the dependent variable, generally a quantity or
percentage.
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Area graphs can chart multiple data sets, each represented by a single layer in
the graph, with as many data points as are meaningful.
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Negative data points are ignored and not shown.
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If you don't supply an X position for each data point, Graphics Server
automatically places points at increments of 1, starting at 0.
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2D area graphs can be drawn with a logarithmic Y axis. This form is sometimes
called a "rate-of-change" graph because it often reveals whether the pace of
growth is increasing, decreasing or remaining steady.
In an absolute area graph, each data set
is drawn from the base line, with subsequent sets drawn in front
of previous ones.
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The stacked percentage area graph shows
each data set as a percentage of the sum of all sets.
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2D area graphs can be drawn with a logarithmically
scaled Y axis.
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Use an area graph...
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To show the trend of one or more data sets over time or another continuous
scale, with an emphasis on quantities.
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In cumulative form when you want to compare each data set to the sum of all
sets.
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In percentage form when you want to view trends in the percentage breakdown of
the sum of data sets.
Other graph types to consider
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If you want to emphasize trends themselves (the downward or upward movement of
values) over quantities, use a line graph.
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If you want data points to stand as separate entities rather than flowing
together, consider a stacked bar graph or stacked
percentage bar graph rather than a cumulative or
percentage area graph.
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