An ergonomic pointing device, such as a mouse, includes a wheel to provide an input signal in addition to X and Y position signals provided by a rotatable ball of a standard mouse. The wheel extends from an upper surface of the pointing device and may be rotated and depressed by the finger of the user, the wheel being positioned and configured to allow a user to activate the wheel while maintaining a finger in a biomechanically neutral position. The mouse is coupled to a computer having a visual display device capable of displaying a data file having adjustable display characteristics. As a user rotates the roller, the mouse generates computer signals that are interpreted by an operating system and software applications running on the computer. The signals generated by the roller, together with a given software application, can be used in spatial navigation. In spatial navigation, a user rotates the roller to cause the computer and the visual display to zoom into and out of the document and thereby display increasing or decreasing magnification levels of the document on the display.