Icons are intended to be unambiguous. Following a set of guidelines can help ensure that icons are designed in an interpretable manner. Icons should be understandable, explicit, informative, distinct, memorable, coherent, familiar, legible, few, compact, attractive, and extensible (Horton, 1996, pp. 371-372).
Horton developed a checklist based on his philosophy (Horton, 1996, pp. 371-372). It is a tool for designers to ensure that their icons are designed properly.
Understandability is a measure of one’s capacity to make sense of an abstract figure. Icons are visual representations, and this indicates how well a viewer can interpret the message (Horton, 1996, pp. 371-372). If an image is accompanied by a label, it, too, will need to be clear.
Unambiguous icons typically demonstrate only one concept, and each concept should only be associated with one image (Horton, 1996, pp. 371-372). He proposes using additional signs or symbols on icons to clarify any remaining uncertainty of the icon’s meaning. An explicit icon is unmistakably clear and understandable. It may have emphasized features or contain certain elements that would make the image more identifiable.
Informative icons illustrate their function. The action or motive the icon represents should be entirely clear so the viewer is not taken by surprise (Horton, 1996, pp. 371-372). The icon should serve some importance. If it is in with a group of others, it should be distinguished in some way. If it is a button on a software program or a symbol on a bathroom door, the function should match the representation.
A distinct icon is identifiable and easy to differentiate when among other similar symbols (Horton, 1996, pp. 371-372). A symbol with an arrow may be unclear but if mixed in with a group of icons with the same arrow in different directions, the meaning may become clear. Sometimes the figures should have distinguishing features that make it unmistakable such as increasing the size of certain features or highlighting a particular part with a different color.
Memorability is significant in most cases. The better one can remember an icon and associate it with a meaning, the more understandable it is (Horton, 1996, pp. 371-372). The image should be vivid and, in some cases, associated with a label for further clarity.
Coherency is an issue with many icons. It should be obvious that an icon is its own symbol and not part of any other icon or part of an overall aesthetic design (Horton, 1996, pp. 371-372). The symbol should have a level of detail necessary to inspire the proper interpretation. Many icons are excessively detailed or far too caricatured to be understandable.
Familiarity is frequently practiced in icon design. An icon may represent a common object, such as a phone, and possibly serve a similar function to its realistic counterpart (Horton, 1996, pp. 371-372). Clicking a phone icon will probably open a communication program or display a phone number. However, people may be able to identify an old-fashioned rotary phone more easily than the silhouette of a modern cellular device, as the rotary phone has a distinct shape and most users are familiar with that technology.
Legibility makes an icon easier to view. If the shapes and lines are distinct and figure contrasts with ground, the icon will be much easier to see (Horton, 1996, pp. 371-372). Some icons will be seen in unusual conditions, such as if the monitor has a better or worse than usual resolution, environmental factors cause visual disturbances, or the viewer has a vision impairment or is too far or too close to the monitor to view it properly. Legibility accounts for these conditions, making the icon visible in virtually any setting.
The fewer icons used the better. All icons should be necessary and relevant to the task (Horton, 1996). Horton states that designers should use 20 or fewer icons per group, but the psychological rule of chunking suggests no more than nine groups. The meaning or function of all icons should be detailed in an external manual or guide (Horton, 1996, pp. 371-372).
An icon is compact if every shape and detail in the image is necessary. All superfluous pixels, including borders, added details, and colors should be eliminated (Horton, 1996, pp. 371-372). Some icons are better represented by words. If the icon takes up more real estate or is too ambiguous, using words may be the best approach.
Attractiveness is important to the overall visual appeal of the system. The icon should be clear and crisp and match the format of the surrounding graphical details (Horton, 1996, pp. 371-372). It should obey a color scheme and share properties with the style such as fonts, rounded corners, or line thicknesses. The images should flow and seem like they belong in the space allotted.
An image’s extensibility will aid the icon’s versatility. If the image can be resized and still be recognized or changed to a black-and-white or more simplistic representation and still hold its original meaning, it is extensible (Horton, 1996, pp. 371-372). The flexibility of an image may also be an asset if it is used in other media or in multiple places. It may also serve other purposes in different disciplines.
Not on Horton’s checklist is a determinant for how long it takes the observer to interpret an image. Clear images should take a short time to identify or label. An image may be clear and obvious, but the user may stare at the icon for a while trying to decide between two definite terms. Comprehensible icons are instantly recognizable and interpretable.
Horton, W. (1994). The icon book: Visual symbols for computer systems and documentation (pp. 262, 245, 249, 260). Toronto: John Wiley & Sons.
Horton, W. (1996). Designing icons and visual symbols. Conference on Human Factors in Computing Systems, 371 – 372. doi:10.1145/257089.257378