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The Playfair Plot
Linegraphs are most commonly used to represent data which changes over time (stock prices or currency values are typical) but may be used wherever pairs of X and Y values are joined by lines.
This chart (quoted in Tufte’s first book) was first used in 1760 to show the rising national debt in England. There are quite a lot of properties to set here, but it is tedious rather than hard, to get the feel of the original graphic.
The most interesting design feature is the x-tick spacing where significant historical dates have been used to mark the years. The Y-axis is intentionally over-scaled to reduce the political impact of the graphic! Playfair’s first draft of this chart was much more dramatic. Opacity is used to give the effect of a water-color wash as used in the original drawing.
SharpPlot sp = new SharpPlot();
years = new int[] {1688,1701,1714,1727,1739,1748,1755,1762,1775,1784};
debt = new double[] {0.2,1.3,3.2,2.4,2.1,3,2.2,4.8,4.4,9.2};
sp.LineGraphStyle = LineGraphStyles.SurfaceShading|LineGraphStyles.ValueTags;
sp.SetMargins(24,36,12,24);
sp.XAxisStyle = XAxisStyles.GridLines;
sp.YAxisStyle = YAxisStyles.GridLines|YAxisStyles.RightAxis;
sp.SetHeadingFont("times",12,FontStyle.Bold|FontStyle.Italic);
sp.SetGridLineStyle(Color.LightGray,LineStyle.Solid,0.3);
sp.SetDatumLineStyle(Color.LightGray,LineStyle.Solid,1.5);
sp.SetXTickMarks(years);
sp.SetYRange(20);
sp.SetYTickMarks(1);
sp.SetFillStyles(FillStyle.Opacity42);
sp.Heading = "Interest of the NATIONAL DEBT from the Revolution";
sp.SetYDatumLines(10);
vtags = new string[]{"Revolution","Accession of Queen Anne","Accession of George 1st",
"Accession of George 2nd","Beginning of Spanish War","End of Spanish War","Beginning of Continental War",
"End of Continental War","Beginning of American War","End of American War"};
sp.SetValueTags(vtags);
sp.SetValueFont("Times",6,FontStyle.Regular,Color.Red);
sp.ValueTagStyle = ValueTagStyles.Vertical;
sp.DrawLineGraph(debt,years);
See also
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