We live just on the border of St Dunstan’s and are new to Canterbury, so I don’t know the boundaries either (but I can ask whether it is ward, parish, or something else). 
The Grade II listed memorial is the grave of the author Joseph Conrad. I’ll see if I can figure out how to use those other tools to work on this map, although I’m still trying to figure out how to embed it into our Cemetery Friends Group. This is all very new to me!