By default, a grid of dots is displayed on the work area, in order to help with symbol with alignment. Toggling this tick box switches the grid on and off.
To the right of the Grid tick box is the snap to grid size selection. This defaults to 10 pt. This determines the intervals at which a released shape or connector will snap to match up with the grid lines. Increasing this number to, for instance, 100 pt will mean that shapes and connectors will only be placed at those that larger intervals. Decreasing this number again will allow you to place shapes with greater precision.interval.
By default, when moving symbols around the work area, guide lines are automatically displayed whenever a central axis or edge align shape boundary aligns with that of another nearby shape. This is to make it easier to align symbols shapes relative to one another. In the example below, one rectangle is being dragged by the user; its edge is currently aligned with the central axis of the other rectangle.
Toggling this tick box switches guidelines on and off.