* Make sure the 3D Editor toolbar is already added to your display. Click Customize > Toolbars if you need to add it.
    * Digitizing 3D feature vertices is supported for points, lines, and polygons.

Steps:

   1. Start ArcScene or ArcGlobe and add the 3D feature class (**pointZ, lineZ, polygonZ**) you want to create new features for.
   2. Add any other base layers you need to complete your digitizing. For example, any surface or building (extruded polygons or multipatches) layers on which you want to place the new 3D feature vertices.
   3. Optionally add any imagery that you want to use as the backdrop for digitizing. Sometimes an image draped on the surface can make the view more realistic.
   4. **On the 3D Editor toolbar**, click the 3D Editor drop-down and click Start Editing.
      If the layers in your table of contents come from more than one source, you may be prompted to choose the layer or workspace to edit.
   5. If you prefer, now would be a good time to open the Snapping Environment window to set snapping properties. Open the window by clicking 3D Editor, expand the Snapping side menu, then click Snapping window.
   6. Choose a feature template and select the edit construction tool from the Create Features window.
      Be sure to click within the extent of your work area. If you are zoomed out too far from the layer's extent, the feature vertex will not be created.
      Use CTRL+Z at any time to undo the last edit, for example, to remove the last segment of the line you just digitized.

![Digitizing in 3D][1]

(can be negative=underground vaules) 

Finally >> **[Convert to 2D Polyline][2]**


  [1]: https://i.sstatic.net/QD4Zn.png
  [2]: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Layer_3D_To_Feature_Class/00q900000083000000/