What are design illustrations?
An illustration is a creative visual expression/interpretation/explanation of an idea/concept/emotion. We can relate illustrations with art/drawing. For example, the pictures carried in an article published in a periodical falls into the category of design illustrations.

Difference between illustrations and graphic design
The difference between design illustrations and graphic designs is nuanced; the major one being the purpose with which they are created. While the former’s role is to explain/interpret a certain idea/text, the latter is expected to communicate with a certain target audience and achieve a specific objective and therefore it is more holistic. For example, while illustration helps in conveying a particular emotion or a fad within the communication piece, graphic design pertains to the overall layout, organization, compositions, images and texts, leading to impactful messaging. The former is more of an artistic expression while the latter is mostly commercial in nature.
Having said that, let’s also understand that in the current era of fast paced life, users are impatient and they tend to spend much less time on reading/watching/listening and understanding the gist of the communication, as they used to do earlier. The initial three seconds are crucial for any communication to engage the users for a longer duration of time. Therefore, creative/artistic expressions are becoming part of communications to make them more interesting, memorable and impactful. As a result, the lines separating illustration and graphic design are getting blurred these days.

Impact of illustrations on human psychology

• Reduction in burden on memory - reading and understanding text puts cognitive load on the human mind, which delays their response

• Faster processing - humans process images 60,000 times faster than the text. Hence it improves information processing (as per the research done by 3M corporation)

• Long lasting - information in the form of visuals can be stored for a longer period in human memory

• Creates interest - communication comprising of color, shapes and other visual elements break monotony, removes boredom and arouses interest

• Promotes simplicity and uniqueness - text (alone) introduces complexity and it may be difficult to understand for many users. Illustrations transform a complex phenomenon into a simplified picture which might be unique in style and easy to comprehend

Illustration vs. storyboard
A number of people mistake illustrations for storyboards and use these two terms interchangeably. However, there is a significant difference between these terms and they serve their own purpose in design.
The storyboard is nothing but a composition of visuals to portray a narration, scene or process. Storyboards have a series of scenes, panels or screens to define a user journey or process, whereas illustrations are restricted to one scene only. Storyboards can be described as a series of illustrations with each scene having a narration. These narrations don’t work independently though - they are connected to each other to complete the story/define the whole process.
Storyboards create a balance between visuals and text to make users understand the process. Some storyboards can be very rough and simple; other times, they can be very elaborate, depending upon the situation - how much time you have, and what stakeholders (your team, clients, etc.) are looking to use them for (more on that later). Storyboards are sequential, situational and present a story, whereas illustrations are scenes of that story which highlight the details and drama happening in those scenes.

Conclusion

• The illustrations are more artistic in nature and limited in purpose while graphic designs are commercial, having a number of larger purposes such as advertising, branding and marketing/ promotion

• Illustrations can enhance the impact of communications and help in connecting with the audience to convey the message better and faster. They can play meaningful roles in standalone graphic design/communication pieces, storyboards as well as live digital assets such as websites

• A series of illustrations can help the audience comprehend the user journey and usability of the product, in the context of interaction design