3D
3D is making something in three dimensions. Rather than just having a width and height like our usual 2D illustrations, 3D also has depth and the ability to rotate and to be seen at different angles.
Using 3D should be considered when there is complex subject matter that is difficult to represent in two dimensions. Adding the third dimension to our art should also add better understanding for the student. Some examples of 3D include an object that has depth to it that also needs to rotate, an object that has depth to it that needs to have a cut-away to show the inside, or an object with depth to it that has multiple pieces that need to be shown separately and working together. It can also be considered when representing the materials of an object in a realistic way is important to being able to understand the subject matter, or when it would be helpful for the viewer to be able to directly interact with the object.
Before choosing to go with 3D, making the subject matter in 2D should always be considered first. 3D is a more time consuming process, but can provide tremendous educational benefits for those illustrations that simply cannot portray something moving in the third dimension.
The process to 3D is similar to illustration and motion design. It just replaces the 2D elements with 3D and might take some more thorough communication between artists and IDs.
When to use
When the addition of depth to an image would be beneficial to the student's understanding of a subject.
When realistic materials are important to understanding the subject.
When motion in a third dimension is difficult or even impossible to portray using only two dimensions.