Choosing the Right Chart

You have three charts of the same nitrate data, a bar chart, a line chart, and a map, and thirty seconds to choose one for the front page of the annual Bluewater Basin report. Your supervisor's rule: 'the chart type is an argument. Choose the one that makes the true argument obvious, not just the one that looks most familiar.'

Different chart types make different comparisons easy and others hard. A line chart makes trends over time obvious. A bar chart makes comparing discrete categories obvious. A map makes spatial patterns obvious. Using the wrong type doesn't just look worse, it can hide the very pattern you're trying to show, or accidentally suggest a pattern that isn't really there.

Picking a chart type is like picking a tool from a toolbox. A hammer and a screwdriver can both technically hit a nail, but only one does it well. Line charts, bar charts, and maps are different tools built for different jobs, and grabbing the wrong one makes the work harder and the result worse.

Data visualization researchers have shown repeatedly that chart type measurably changes how accurately readers perceive relationships in the same underlying data. Choosing chart type deliberately, rather than by habit, is now considered a core scientific communication skill, not just a design preference.

Explain to someone why chart type choice is 'an argument' and not just a stylistic decision.