I have lines from AutoCAD of bathymetry data, imported into ArcMap. It is spatially referenced, however the contour lines do not have Z-values associated with them. I have a paper copy of the map, and would like to assign the values to the lines manually. However, simply creating a field in the attribute table isn't enough...I would like Arc to recognise those values as the actual 3D elevation. How can I do this?