Thanks, Jez.  The process for this feature was as follows:

- I know there's a ditch called "drain number 3" in the area, and its approximate course, from the map accompanying the inclosure award for Sawston (1809, so definitely out of copyright).
- I confirm that the ditch still exists, and still follows the same approximate course, from the map on the CCC website (I think that probably is OS basemap data, although I can't be sure because I don't have access to the unadulterated OS basemap.)
- I mark the exact course by drawing a line following the linear feature that's visible in the satellite imagery provided on iD.

What do you think?  Is that an acceptable procedure?
