How do I stitch rectangular terrain surfaces to roads?

I have a road that I'm adding a terrain surface to. If I create the surface as a rectangle (4 straight edges) the terrain does NOT stitch to the road. If the terrain surface has one edge curved (in my mind it becomes blob-like) then the stitching process works. Will try to attach the screenshots to this message.

Is there a way to get proper stitching with a rectangular terrain surface?

Thx

Answer 1

[Shawn Allen]

Turns out ctrl-click on perimeter vertices and road vertices will do what I wanted.