Both Layers and Groups are essential Illustrator features that help keep complex drawings organized and easier to work with.
Unfortunately, Illustrator doesn't let you truly combine the features. That is, if you select items that live on different layers, and then choose Object > Group (in order to treat them as a single unit for selecting, moving and transforming), Illustrator moves all of the selected elements into sublayers of the topmost selected item's layer.
Sometimes that's okay. More often, it's not — after all, you took care to create multiple layers and place your artwork on them for a reason, right? Now they've been moved. The next time you choose to hide or lock a layer, you'll get a different result than what you intended.
Worse, moving objects to different layers changes their stacking order, and you may not be happy with how some of the elements you grouped now overlap elements they used to be in back of.
Solution: Save the Selection
The next time you're faced with the dilemma of grouping objects in different layers, *don't* group them. You can achieve most of a group's benefits by using the Save Selection feature instead. Select all the items you were about to group, choose Select > Save Selection, name the selection in the dialog box, then click OK.
Didn't even know Illustrator had that feature, did you? It's a quiet one, that's for sure. But it's been part of Illustrator since CS1.
Go ahead and deselect and go about your business. The next time you want to manipulate the "group," go to the Select menu and choose the selection's name. (All saved selection names appear at the bottom of the Select menu, quite handy.) Illustrator remembers which objects were part of the selection — even if you've moved or transformed any of them, even if you change which layers they were on — and reselects them for you.
Now you can drag the multiple selection around as usual. If you want to scale the selection (as you would to a group), just hover over a handle of the selection's bounding box to see the scale arrows and drag. To rotate the selection, put your cursor slightly outside of the bounding box so you see the curved "rotate" arrow and then drag.
If you don't see a bounding box, choose View > Show Bounding Box, or press the "E" key — the Free Transform tool — to put one there temporarily.
Of course you can use the fields in the Transform panel or Control panel to do precise transformations as well.
Give Your Selection a Keyboard Shortcut
What's nice about an actual Group is that to select all of its objects, you just have to click on any of its component objects. A named selection isn't a group, so with nothing selected, clicking on one of its objects selects just that object. You always have to choose the name of the saved selection from the Select menu to recall the entire selection.
An occasional trip to the Select menu is no big deal, but I can see how it can really cramp your style if you're dealing with lots of saved selections or you repeatedly have to select the same one.
If that's the case, consider assigning a keyboard shortcut to one or more of your named selections. That way you can just press the shortcut, and voila, your "group" is reselected. While the selection names don't show up in Edit > Keyboard Shortcuts, it's ten seconds' work to assign one with an Action (Window > Actions), even if you've never used Actions before.
Create a new action (click the New Action button at the bottom of the panel), and in the resulting New Action dialog box, name it and give it a keyboard shortcut. Click the Record button in the dialog box to close it and start recording your action.
The first time I ever recorded an Action, I thought I had to move as quickly as I wanted the finished Action to play. Heh … not true! Take your time. Go have a cup of coffee if you want. Illustrator is only going to record the things you do, not the time it takes you to do them. (It's called "Actions," remember.) It will play your actions back as fast as your computer permits.
Done with your coffee? Okay. Resist the temptation to go immediately to the Select menu so Illustrator can record that. Choosing the name of a selection you saved is unfortunately not one of things that Illustrator records as you do it, so don't bother.
Instead, while the action is recording, open the Action panel's fly-out menu and choose Insert Menu Item. Now you can go to the Select menu and when you choose the named selection, its name appears in the Insert Menu Item dialog box. Click OK to close the dialog, then click the Stop Recording icon (the black square) at the bottom of the Actions panel.
Test it out — deselect everything, then press the keyboard shortcut you assigned. There's your "group," all selected, on their original layers so the stacking order is intact.
Whether or not you assign a keyboard shortcut to a named selection,
don't forget the feature itself. Saved selections are fantastically
useful throughout the program. I wish every program had the feature!