Edges and corners have unbounded width in the direction of movement
Aliases: screen edge · edge target
What it is
A target on a screen edge has approximately infinite effective width in movement toward that edge: the pointer cannot travel beyond the display boundary, so it need not stop at a precise endpoint. This is a geometric implication of Fitts's law for desktop mouse use, not a guarantee that every edge control is usable.
Why it happens
An ordinary target requires stopping within a finite interval; overshooting misses it. A hard display boundary catches the movement, so endpoint error along that axis no longer causes a miss and final correction is reduced. Width parallel to the edge remains finite: several adjacent edge items must still be distinguished.
Studying it
Compare edge and interior targets matched in area and distance, measuring movement time, endpoint distributions, and misses. Control approach direction and target length along the edge, and separate system or menu delays from pointing time. Across displays, gains, and multi-monitor setups, establish that the edge really is an impassable boundary.
Where it stops holding
The effect requires a pointer stopped by a hard edge. Touchscreens, borderless windows, full-screen gesture zones, continuous multi-display movement, and remote desktops can weaken or remove that constraint. An edge may also be unavailable when a window is not maximized or the operating system reserves it for a gesture.
Applying it
- In mouse-led desktop work, place frequent, independent actions on stable display edges and ensure their hit areas extend to the boundary.
- Do not pack many tiny actions along one edge; each still needs enough length along the edge to be distinguished.
- Test actual window and monitor configurations to verify the pointer is caught rather than crossing to another display or a system zone.