Now, you can see the coordinates at the bottom right. The coordinates are what you really need right now. Leave them down in that bottom corner and unselect your edge of the CY by clicking again on the Edge button. Click on the plane you made earlier and click on the edge button. Refer to Figure 7.

 Figure 7

You can see that the plane's edge and the Construction Yard's lower edge are matched up properly. You eliminate clipping errors this way. Clipping errors are those annoying holes in terrain that do not belong there. For each side of the Construction Yard, do the same until you have finished the terrain matching to the CY. It shouldn't be difficult, although it is a bit time consuming.