The diagonal right button is for intersections with more than two crossing streets and other situations where it may best represent the direction available. Clicking this button moves you one position in that direction, reorienting your view to point in that direction. In some cases there could be a scenic view or close up button in this spot.
Scenic views are high resolution views of special interest.
Close up views are for reading historical markers. Normally you will see the blank icon in this position, meaning that there are no options in this direction.