This halo-enhanced map shows five arcs, each
indicating the location of one restaurant located off-screen
(this figure uses a translucent overlay to show the actual
locations of the restaurants). The higher curvature of the
arc at the bottom right allows users to conclude that this
restaurant is closer than the others.
As users pan and zoom, display content can
disappear into off-screen space, particularly on small-screen devices.
The clipping of locations, such as relevant places on a map, can make
spatial cognition tasks harder. Halo is a visualization technique that
supports spatial cognition by showing users the location of off-screen
objects. Halo accomplishes this by surrounding off-screen objects with
rings that are just large enough to reach into the border region of the
display window. From the portion of the ring that is visible on-screen,
users can infer the off-screen location of the object at the center of
the ring. We have conducted a user study comparing Halo with an
arrow-based visualization technique with respect to four types of
map-based route planning tasks. When using the Halo interface, users
completed tasks 16-33% faster, while there were no significant
differences in error rate for three out of four tasks in our study.