Browsing large information spaces such as maps on the limited
screen of mobile devices often requires people to perform panning
and zooming operations that move relevant display content offscreen.
This makes it difficult to perform spatial tasks such as
finding the location of Points Of Interest (POIs) in a city.
Visualizing the location of off-screen objects can mitigate this
problem: in this paper, we present a user study comparing the
Halo [2] approach with two other techniques based on arrows.
Halo surrounds off-screen objects with circles that reach the
display window, so that users can derive the location and distance
of objects by observing the visible portion of the corresponding
circles. In the two arrow-based techniques, arrows point at objects
and their size and body length, respectively, inform about the
distance of objects. Our study involved four tasks requiring users
to identify and compare off-screen objects locations, and also
investigated the effectiveness of the three techniques with respect
to the number of off-screen objects. Arrows allowed users to
order off-screen objects faster and more accurately according to
their distance, while Halo allowed users to better identify the
correct location of off-screen objects. Implications of these results
for mobile map-based applications are also discussed.
