Using snapping, you can open a background map and designate its layer as the snap/grab target. When a layer is designated as the snap/grab target, the features on the layer and the geometries of the features can be used to create new reference model features.
The vertices of your new or existing feature need to match the points of a surface feature in your reference model. This means that the Surfaces layer needs to be designated as the snap/grab target.
To use snapping:
1. In the Layers window right-click the desired model feature layer and, from the pop-up menu, select Set as Snap/Grab Target.
OR
from the Active grab/snap layer drop-down list in the toolbar, select the desired model feature layer.
2. Click the mouse button to place a new vertex.
3. [Optional] To position the vertex over an existing point:
• click and hold the mouse button,
• press and hold the <Shift> key and the <S> (snap) OR <I> (snap-intersect) key
• drag the cursor.
As you drag, you will see a point moving with the cursor, which will change in style as you pass over vertices and nodes in the snap target. When you get within a few pixels of a vertex in the surface, the cursor will automatically snap to the vertex.
4. Release the mouse button to place the point.
The point is placed in the exact location of the selected vertex. To snap additional points, keep the <Shift> and the <S> or the <I> key pressed and continue clicking until all of the points for the feature have been created.