Algorithm 2 Computation of track spread
	Data: User’s trajectory data (pos = (x, y), array)
	Results: Track spread (ts) feature
1	track_spread_array ← [], i = 1
2	track_center ← (mean (pos(x)), mean (pos(y)))
3	while i < length(pos) do
4		distance ← √(posi(x) − track_center(x))2 + (posi(y) − track_center(y))2
5		track_spread_array ← (ti − ti−1)
6	end
7	ts ← max (track_spread_array)
8	end