Preposition or position is indicated by a red/grey ball relative to other elements. Prepositions on their own may seem abstract but when learnt as a set the reader will be able to identify the red ball and make sense of its position.
The red is also used alongside other parts of the symbol to highlight a feature or relationship such as foreground to background.
There are several different uses of arrows. These are used to indicate various concepts such as direction, motion, actions and time or indicate the pertinent part of a symbol.