In a city, protecting units like police cars move around and protect places such as banks and
residential buildings. Different places may have different requirements in how many
protecting units should be nearby. If any place has less protecting units around than it
requires, it is an unsafe place. This paper studies the Continuous Top-k Unsafe Places
(CTUP) query, which continuously monitors the k least safe places while the protecting units
keep sending their location updates to the server. The CTUP query is a novel addition to the …

In a city, protecting units like police cars move around and protect places such as banks and
residential buildings. Different places may have different requirements in how many
protecting units should be nearby. If any place has less protecting units around than it
requires, it is an unsafe place.