Choosing the right chart type (II)

This posts concludes the previous post on choosing a chart type and describes the categories relationship/correlation and frequency/ranking.

Relationship/correlation

A relationship between two dimensions is often displayed with a scatter chart. For instance sales growth of products can be plotted in relation to their profitability. A bubble charts adds a third dimension to the visual data. So for the sales numbers the size of each bubble could represent last year’s sales volume.

In some scenarios a correlation between two dimensions may be expected that would be visible in the scatter or bubble chart. Imagine that management realigned sales incentives to focus on the most profitable products. Hopefully, this results in a positive correlation between sales growth and product profitability. For this application some charting tools allow you to automatically insert a trend line for subsets or all data points.

Scatter chart sample

Scatter chart sample: Relationship GDP/Olympic medal count

Another chart type that may be useful to relate two dimensions is a bar-mekko. Effectively, this is a column chart with variable column widths. Or a Marimekko without a 100% axis to put it another way. This could be another way display the sales data with the column width depicting revenue and its height profitability. For a limited of categories, say products in this case, this type may be easier to read than a scatter chart. At the same time it describes a composition, e.g. how the company sales are split between products.

Frequency or ranking

This category is for you if data needs to be presented for multiple items but it is not desirable or possible to combine the numbers to a composite value. A typical application would be a histogram or a distribution curve if displaying many data points. Opposed to a composition chart, median or quartile information can easily be highlighted. This again shows that it’s not primarily about the data you want to show but the point that you want to make.

If columns are ordered by their frequency values the result will be a ranking chart. Values will be displayed from highest to lowest or vice versa. To visually display which are the “top” values it may be a good idea to rotate the chart to a bar charts with the best items standing literally at the top. Of course, frequency can be substituted by any other value describing the quality of an item.

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