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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);

Worked Examples

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