Book Series Begins on User Interface Design

BFMA is extremely fortunate to have a long-standing relationship with one of the most respected authorities on user interface design, Mr. Bill Galitz.  He has recently published the third edition of The Essential Guide to User Interface Design (2007, Wiley Publishing Company, Indianapolis, Indiana, 857 pages). 

Wilbert (Bill) O. Galitz is an internationally respected consultant, author, and instructor with a long and illustrious career in human factors and user-interface design. For many years he conducted a screen design course for BFMA.  Click here for a complete biography.

The article below is the first in a series and is derived from the author’s most recent book, The Essential Guide to User Interface Design.  You can order this book from BFMA.

Fitts’ Law

A common activity in screen or Web page design involves moving a pointer over the screen (using a device such as a mouse or trackball), positioning the pointer over an object or button, and then making a selection to implement the action or the choice presented. A common failing of many screens is inadequately sized buttons for easy human selection. I have seen many pages with buttons scarcely larger than the letter "o" in this article. (In spite of sufficient available space on the page.)

In 1954 a researcher named Paul Fitts studied the relationship between speed of human motor movements and the size and distance of an intended target. The results of this study have since been referred as Fitts’ Law.

Fitts’ Law states that the time to acquire a target is a function of the distance to and size of the target. This simply means that the bigger the target is, or the closer the target is, the faster it will be reached. The implications in design are as follows:

Provide large buttons or objects for important functions. Big buttons are better than small buttons. They provide a larger target for the user to access with the screen pointer. Large buttons reduce the need for very precise hand positioning movements.

Locate buttons or objects in the logical sequence of user activities whenever possible. Buttons positioned in the logical sequence of events always result in shorter pointer movements

Take advantage of the "pinning" actions of the sides, top, bottom, and corners of the screen. Create toolbar icons that "bleed" into the edges of a display, rather than those that leave a one-pixel, nonclickable edge along the display boundary. The edge of the screen will stop or "pin" the pointer’s movement at a position over the toolbar, permitting much faster movement to the toolbar. A one-pixel edge will require more careful positioning of the pointer over the toolbar.

Fitts’ Law is one of the most "common-sense" rules for interface design. Tiny and improperly positioned buttons always reduce user speed and increase selection errors. Adequately sized and properly positioned buttons will make the user’s task much easier.

Reference
Fitts, P.M. (1954). "The information capacity of the human motor system in controlling the amplitude of movement." Journal of Experimental Psychology, 47, 381-391.