The Main Idea 

A heat map is a visual display of data in the form of a map or diagram in which data values are grouped into different colors.

A bubble map is another type of data visualization in which differently-sized bubbles are placed on a map. Shading may be used to represent a second variable in the data set.

These types of displays are common in the media. Reading or interpreting the information presented in a complex display can be challenging. Always look for a guide to how the display has arranged the data, called a legend or a key. The legend of a map is the description, explanation, or table of symbols printed on the map to aid readers to understand and interpret the map better.

Please see the following video for an explanation of how to read and interpret these types of complex graphical displays.

Misleading graphs are sometimes created to intentionally misrepresent the data.

• Always check the scale of a graph to be sure it provides a picture complete enough from which you can draw a conclusion.
• Ask yourself: “What information is this graph missing?” Some graphs are missing a vertical axis or contain two vertical axes with scales that are not equivalent.

Key components that should be present in a graphical display:

• Horizontal axis
• Vertical axis
• Clear data lines
• Distinct bars
• A color legend

The Gestalt Principles for data visualization are:

• Design attributes (color, symbols, and lines/curves) should be used appropriately.

• Precision requires the vertical axis to begin at 0 and not some other number.

• Efficiency requires that the effort it takes a reader to understand the display should be minimized.

• Time, ink, and space should be used so that the reader can obtain the largest number of ideas in the shortest time with the least amount of ink in the smallest space.

Multivariate graphical displays encourage the reader to make comparisons through the use of similarity, proximity, continuity, or closure.

• Similarity is the use of similar colors or shapes.
• Proximity is the spacing between visual objects.
• Connection or continuity creates visual focus for the eyes using lines.
• Closure is the practice of using boxes or circles to highlight groups.