There are three design principles for creating effective charts and visualizations.

Appropriate

The appropriate chart should be used for the intended analysis. Choosing the right chart is critical for supporting the end-users analysis needs.

Accurate

The design of the chart should convey an accurate perception of the data.  Sorting, aspect ratios, axis and trend lines should all provide support for the correct interpretation of the data. 

Usable

Charts should be easy to use, and designed so that results are easy to understand and interpret.