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Visual Studio Magazine Reader's Choice Award Winner

Using Scale Breaks

Introduction

In the never ending endeavor to make your charts more readable, Dundas Software has incorporated scale breaks into Dundas Chart for .NET version 5.5 and above. This powerful technology allows you to customize your chart so that large differences between the high and low values of the data being plotted does not ruin the readability of your chart. Put a different way, scale breaks are intentional breaks in the y-axis used to redistribute data points within a chart. Adding scale breaks to your chart can result in much better legibility.


Figure 1: Chart without scale breaks
Figure 2: Chart with scale breaks

In Figure 1 it is very difficult to read most of the data as it is squished and illegible. Compare this to Figure 2 which has scale breaks enabled and is far more legible.

Features

While the default look and feel of scale breaks is sufficient for most users, there are a number of properties you can change to customize it.


Figure 3: Chart with default scale breaks

The first thing most people would want to customize is the look of the scale breaks. There are a number of options available for this, including the width and color of the line, the space of the break, and the overall look. As said previously, Figure 3 contains default scale breaks which means the width of the lines is 1, the color is black, the spacing is 1.5 (this value will be explained later) and the overall look is ragged. Below are a few different possible variations of these properties.


Figure 4: Scale breaks with red lines
Figure 5: Wavy line scale breaks

Figure 6: Straight line scale breaks
Figure 7: No line scale breaks

Figure 8: Scale breaks with space set to 3
Figure 9: Scale breaks with a combination of changes

Using scale breaks

By default, scale breaks are disabled. The first step in using scale breaks is to enable them by setting the ScaleBreakStyle.Enabled property to True. Once scale breaks are enabled, you will see the default look (shown in Figure 3) on your chart.

There are 3 properties relating to how the scale break lines look. The first is ScaleBreakStyle.LineColor, which controls the color of the lines. The second is ScaleBreakStyle.LineStyle which controls how the line is drawn (i.e. solid, dashed, dotted). The last is ScaleBreakStyle.LineWidth which specifies the width of the line in pixel value. The spacing between the scale break lines is controlled by the property ScaleBreakStyle.Spacing, and takes a value that is calculated as a percentage of the y-axis scale. Lastly, the overall look of scale breaks is controlled by the ScaleBreakStyle.BreakLineType property which has four options: wavy, ragged, straight or none. The configuration of these properties would typically look something like:

//Change the color of the line to red
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.LineColor = Color.Red;

//Change the style of the line
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.LineStyle = ChartDashStyle.Solid;

//Change the width of the line
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.LineWidth = 2;

//Change the spacing between the scale break lines
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.Spacing = 2;

//Change the overall look to wavy scale breaks type
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.BreakLineType=BreakLineType.Wavy;

As well as changing how the scale break lines look, you can also control the tolerance of scale breaks through the property ScaleBreakStyle.CollapsibleSpaceThreshold. The tolerance is measured as a percentage of the y-axis scale, so if it is set to 25 (its default value) then data points must have a difference of at least 25% of the scale for a scale break to occur. As well, there can only be a maximum of 2 scale breaks by default, but this can be modified through the ScaleBreakStyle.MaxNumberOfBreaks property. Lastly, it is also possible to define whether or not the y-axis scale will start from zero or a calculated value through the ScaleBreakStyle.StartFromZero property, which is useful if all data points are significantly far from zero.


Figure 10: StartFromZero set to false

The following is an example demonstrating how to set these properties.

//Set the tolerance to 40% of the y-axis scale
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.CollapsibleSpaceThreshold = 40;

//Set the maximum number of scale breaks to 4
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.MaxNumberOfBreaks = 4;

//Set the scale to start from the minimum value, not zero
Chart1.ChartAreas["Default"].AxisY.ScaleBreakStyle.StartFromZero = AutoBool.False;

Conclusion

Scale breaks are extremely useful for making data in a chart far more legible, and with Dundas Chart for .NET they are easy to use. While this particular article specifies how to change every possible property within scale breaks, most of the time you will not need to change more than one or two of them to get the look you desire. More information is available on scale breaks in the documentation included with Dundas Chart for .NET (version 5.5 and above). Furthermore, feel free to download a full evaluation copy to test our scale breaks feature.