Algorithm 4 Computation of hotspot spread
	Data: User’s trajectory data (pos = (x, y), array)
	Results: Hotspot spread (hs) feature
1	cells ← unique((round (pos(x)), round (pos(y))))
2	hs_center ← (mean (cells(x)), mean (cells(y)))
3	track_center ← (mean (pos(x)), mean (pos(y)))
4	hs ← √(track_center(x) − hs_center(x))2 + (track_center(y) − hs_center(y))2
5	end