Explain the importance of axis scales and labeling in data visualization.
Instruction: Discuss how you decide on the scaling and labeling of axes in your visualizations and its impact on data interpretation.
Updated
Official answer
Axes define how visual distance maps to values. Choose scales from the comparison and label the measure, units, time period and any transformation.
A linear scale uses equal distances for equal absolute differences. A logarithmic scale uses equal distances for equal ratios; ordinary real-valued logs require positive values. Do not silently remove zeros or negative observations to make a log chart work. Explain another transformation if one is needed.
Bar lengths encode magnitude, so use a meaningful zero baseline for ordinary magnitude bars. A line chart can use a narrower range to show variation, but make that range clear and avoid exaggerating a trivial change. Comparable small multiples should normally share scales or visibly disclose differences.
For example, a change from 100 to 110 is ten units and 10%. On a bar axis beginning at 99, the displayed lengths would be 1 and 11, making the second bar appear eleven times as long. The arithmetic has not changed; the visual encoding has.
Use readable tick intervals and unambiguous dates/timezones. Avoid dual axes that imply a relationship merely through arbitrary rescaling. A trend after a launch does not prove a launch effect, regardless of axis choice.