Average horizontal flow speed as a function of the elapsed time. The maps were computed using a Gaussian sampling window with an FWHM = 1200 km and time cadence Δt = 10–480 s. The increasing time cadences Δt are presented as progressively lighter shades of gray. The black solid line is depicting the result for the time cadence Δt = 60 s, which has been identified in Verma & Denker (2011) as an optimal choice for tracking horizontal proper motions in Hinode G-band time-series data.