Canvas: Diagram Layout inspector
Use this inspector to automatically lay out shapes based on the logical relationships established by the connection lines between them.
The five buttons at the top of the inspector are for choosing from the available layout types. The first four are hierarchical layouts that point in different directions, and the last one is a force-directed layout. Force-directed layouts grow in semi-random directions from the center, rather than in one particular direction from the edge.
Use the pop-up menus to determine when objects should be automatically laid out, and which objects should be allowed to be laid out.
Deselect the Animate layout changes checkbox if you'd rather not watch the objects sliding around the canvas.
Click the Lay Out Now button to lay out the graph once now using the current settings on the inspector.
When you use a hierarchical layout, you get Object Order and Object Rank settings.
The Object Order buttons determine how to order items on the same level: reduce line crossings, try to keep their current order, or use objects' back-to-front ordering.
Use the Object Rank buttons to assign a hierarchical rank to the selected objects. Default lets OmniGraffle decide the rank based on connections, Minimum puts the objects at the top of the hierarchy, Maximum puts the objects at the bottom of the hierarchy, and Same makes sure that the objects end up on the same level. These assignments don't change the directions of connection lines, so you can always select all of your objects and choose Default to return them to normal.
When you use a force-directed layout, you get three sliders and a checkbox.
In this kind of layout, connection lines act like springs: they can stretch and compress, but they have a natural length they try to maintain. Drag the Line Length slider to set the natural length of the lines.
The Line Tension slider determines how strongly the lines try to remain at their natural length. Making the line tension stronger than the shape repulsion puts a priority on keeping lines all the same length, regardless of how unevenly distributed the shapes end up.
The Shape Repulsion slider determines how strongly the shapes try to avoid coming near one another. Making the shape repulsion stronger than the line tension puts a priority on spacing out the shapes evenly on the canvas, regardless of how long the lines end up being.
Select Randomize starting locations to mix up all of the shapes before laying them out, for an unbiased distribution. If you have this selected, sometimes it helps to lay out the diagram several times in a row until you get an organization that you like.