When I do a 2D drawing on the top view and the scene contain 3D content, it regularly happens that the points are not aligned. How to re(align) this points without change the top view draw ? Or, how to do a draw on a view with all the points on the same alignment ?
To ‘flatten’ your curves to the Top CPlane, use _ProjectToCPlane _DeleteInput=_Yes.
To keep things flat on the active CPlane while drawing and snapping to other 3D objects, activate the ‘Project’ setting in the Osnap control.
Also, when you are not working on the active CPlane and want to prevent snapping to other geometry, you can use the Tab key (possibly in combination with the Shift key) to lock the direction before snapping to reference geometry. Or snap to reference geometry with the Ctrl key active and then snap to your new geometry in a different viewport.