The "horizontal dimension" refers to our everyday, commonplace, relative reality, in which we can only discern superficial structures. On the horizontal dimension, our daily lives take place - we sleep, go to work, eat, exercise, clean our teeth, and so on. But on this dimension we are also bound in limits such as the Buddhist "Three poisons": greed/attachement, hatred/aversion and delusion/ignorance. The horizontal dimension manifests itself as the four cardinal directions. They are represented by the four blue arrows on the image.
The vertical dimension
The „vertical dimension“ is the spiritual dimension, where there are two fundamental sources of truth and wisdom - the Relative and the Absolute. Reaching towards the vertical dimension, we discover how to break through, balance the above mentioned "Three Poisons" by recognized, integrated and lived wisdom. The white arrow pointing upwards to the heavens connects us to absolute wisdom, whilst the red arrow indicating downwards links us to the earth and its relative wisdom.
So on the level of the Relative we have both - the horizontal dimension, which most people recognize simply as „the world“, and relative wisdom as part of the vertical dimension.