1. What are you trying to accomplish?
This question is very important to answer before you start designing your visualization. Answering this question will help you choose the format that will work for your message.
2. Are you including all of the data that is needed to understand your message?
Sometimes, data visualizations can be misleading if all of the necessary information isn't being represented. You want your viewers to see you as a reliable source. Make sure that you have all of the data needed to understand your message.
3. Do you have a general idea of how different visualization formats work?
While this isn't essential, it is certainly helpful to have a general knowledge of visualization formats before you start plugging your data into different formats to see which works best. This will help you eliminate some formats that wouldn't make sense for your data and hopefully save some time.
In his book, The Truthful Art: Data, Charts, and Maps for Communication, Alberto Cairo gives specific tips for choosing a graph to visually represent your data. When trying to choose a type of visualization for your data it is important to remember that it is a process and that is okay. There are no rules for how you should choose a visualization and no one says that you can only use one. Experiment with visualizations and see which works best for you!
Taken from, The Truthful Art: Data, Charts, and Maps for Communication by Alberto Cairo, pgs.124-125.
"A set of laws arising from the 1920s' psychology, describing how humans typically see objects by grouping similar elements, recognizing patterns and simplifying complex images."- Gestalt Principles from Interaction Design Foundation
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