The drawing on page 3 of the datasheet shows you the direction of the x and y axis. As the comment below the drawing states, it's a top view (looking at the chip soldered on the PCB). The little dot in the top left corner is the pin 1 marker which you should find on the chip also. Turn the PCB so that the dot is in the same corner and the arrows show you the positive direction of the x and y axis.