Design Principles

Besides appropriate chart types, certain design principles can help to immediately show distinctive trends.

Attention Grabbers

Certain retinal encoding can be used as attention grabbers, also known as Pre-attentive Attributes.

_images/preattentive.png

from Udacity’s data visualisation & d3.js course. Note that movement is supposed to have a flickering effect for one of the data points.

Importance of Null Values

It may be useful to use values which are null or zero to highlight certain trends. This is known as Negative Space. An example is John Snow’s Chlorea map, with the Brewy showing no deaths from the disease.

_images/johnsnow.png

from Udacity’s data visualisation & d3.js course.

Keep it Simple

Probably one of the most important design principle which can be summarised as keeping it simple. The aim is to remove all clutter that are not helpful in conveying a message. Such clutter is known as Chart Junk. They only serve to distract users from the data. Some examples include:

  1. Excessive colors for categorical data
  2. Special effects like, 3D and shadows
  3. Too many labels
  4. Distinctive grid lines
  5. Fancy pictures or graphics

The Data-Ink Ratio is a useful concept used to quantify how much clutter is in a chart. Its formula is defined as:

_images/dataink.png

from Udacity’s data visualisation & d3.js course.

A high data-ink ratio means it is a simple and neat chart, while a low ratio signifies a complicated and cluttered chart.

Keep it Honest

It is important to preserve the integrity of the data in a visualisation. There are various ways charts can be manipulated to convey to the end-user a certain message by ‘cheating’. Here are some selected ones to that should be avoided:

  1. 3D effects distorts the scaling
  2. Stretching the proportion by not starting from 0.