I would like to know how to arrange my piano roll to view two regions at once on Apple - Logic Pro 9?
It would be extremely useful for lining up my notes properly between two or more regions.
There's two ways to achieve what you want. From what I understand from your question you want to find out how to view two MIDI regions in piano roll and/or to line up multiple MIDI regions for comparison?
You could open two separate piano roll windows via the Window menu on the Taskbar and resize and move the piano roll windows to your liking. However to achieve what you want to achieve I think it is better off that you hold shift and select multiple MIDI regions. Upon opening your piano roll editor both regions will show up on the same piano roll superimposed. It makes it hard to distinguish which notes are from which region but it allows you to line them up the way you want. Having two separate piano roll windows makes it very hard to accurately compare two midi regions without tracking the playhead during playback - which will only happen during playback.