Examples of the photospheric horizontal velocity maps derived from the SDO/HMI SHARP data taken from Apr. 16, 2012, 12:48 UT to Apr. 18, 2012, 11:24 UT, which is from 24 h before the start of the pore formation to several hour after. The arrows indicate the horizontal velocity; red (light blue) shows the leading (trailing), positive (negative) polarity. In all panels but the first, the studied pore coincides with the largest size structure in the leading region. The magnetic field in the background magnetogram is shown in the range of values specified in the colour bars. The full temporal evolution of all computed maps is shown in a movie available online.