Grid snapping behavior?

I am pretty confused by this. I uncheck Snap to Grid, and it simply makes no difference. Neither do the ctrl and/or cmd keys. Align to Grid seems to work, but then sometimes moving object put it back between the grid lines. It’s not all elements that I can get to snap to the grid correct, but it is all elements that ALWAYS snap.

Should the grid behavior be the same with lines as other objects? If I’d changed the grid resolution at some point and then changed back, would that have any effect on this? I’m not sure exactly that the behavior is supposed to be, but it seems that what’s intuitive here is not happening.


Here’s how it works, or at least how I think it does:

Snap to grid is a global setting. Align to grid is a command that applies to the selected object. The minor gridlines are the snapping targets.
If snapping is on it happens only when you move or resize an object. Aligning happens when you execute the command (menu choice or keystroke). If the grid is changed the object snaps to the new grid when you next move it.
Grid behavior applies to line endpoints.
If snapping is on arrow keys move the selected object one minor grid unit. If snapping is off (or on with option key held down) arrow keys move the selected object one nudge. A nudge is one pixel (in ruler units) at 100% scaling and changes proportionately at other scales. (e.g., 1/2 pixel at 200%, 2 pixels at 50%). It therefore remains the same distance on the screen whatever the scale.

Note that changing ruler units doesn’t change the grid. The gridlines are just relabeled in the new units. E.g., Changing units from inches to mm relabels the grid spacing from 1 to 25.4. You have to change the grid spacing, usually to integer values in the new units, to get the grid itself to change.

Hope this helps.

Thanks for the detailed explanation, and sorry for the delay. I think that’s how expect it to operate also– and sometimes it does. Then I get things like this, where it will move by the grid amount, but not ON the grid lines (and won’t align to them). So there is basically no way to get the thing on the grid:


Those three white dots over the thick vertical line may be a clue. If you were moving a single horizontal line there should be only one. It looks like you could be moving a larger object or group whose boundary (the outer dots) does align with the grid. Is it possible that there’s an invisible object there? If there were, though, we’d see an outline of the whole selection, so it’s still a mystery.