Alt Text for Complex Images/ Data Visuals

Issue

Complex images that contain information/data that can be difficult to describe, but without text alternatives the data is hidden from some users. Complex images include embedded images of data visualizations, such as: 

  • Maps
  • Charts of all types (bar chart, line graph, etc.)
  • Diagrams

What to do

Complex images require a two-part text alternative. This includes a short description (alt text) and a long description to provide a more in-depth description and access to the raw data. 

  • Short Description (alt text)
    • Use the following formula: 
      “[Chart type] of [type of data] where [reason for including chart]”
  • Long Description
    • Provides detailed information about visual content, including scales, values, relationships, and trends.
    • Aims to convey the intended message of the data and helps users understand categories, trends, and extreme values.
    • Artificial Intelligence (AI) tools can help you get started, but a AI-generated description MUST be verified and often edited by a human who knows the data.
    • The most accessible way to provide this information is by publishing it as html and linking to it. Be sure to include a link back to your original content, though.

Recommended tools

Who’s affected

People who:

  • Use screen readers (blind, low vision)
  • Have slow or weak internet (alt text is what shows up on the screen if the image is slow to load)

WCAG standard