Use dynamic guides and snapping
The Canvas dynamic guides and control point snapping help you align selected points with other objects.
Use control point snapping on a shape
Click the View pop-up menu above the right side of the Canvas, and ensure that the Dynamic Guides item is checkmarked.
In the menu bar, choose View > Snap to ensure that snapping is turned on.
When active, a check mark appears next to the menu item.
Select the shape to edit, then click and hold the 2D transform tools pop-up menu in the toolbar and choose the Edit Points tool.
Note: In the Canvas, you can also Control-click a shape and choose Edit Points from the shortcut menu.
In the Canvas, drag a control point.
Yellow guides appear when the selected control point aligns with the edges or center of the original shape, the edges or center of other objects, or the center of the Canvas.
Turn off snapping while editing control points
You can temporarily disable snapping to allow for subtle shape adjustments.
Do one of the following:
Press N to turn off snapping. Press N again to turn snapping back on.
As you begin to move the selected control point, hold down the Command key to turn off snapping as you drag the point.
Specify whether control points snap to the center, edges, or both the center and edges of an object
Choose Motion > Preferences (or press Command-comma).
In the Canvas pane, choose an option from the “Snap Objects At Their” pop-up menu.