Adam,
Many Thanks.
This was my starting point -
http://www.wiki.luftwaffedata.co.uk/wiki/index.php?title=UK_Target_CodesThat was based on something originally from one of the volumes of The Blitz Then and Now .
Its the codes 97 and 98 that I'm interested in.
I would think that the Fishponds codes for Bristol have been built up from the annotations on Luftwaffe Target Photos similar to the ones I am currently looking at and that caused the current question.
By knowing the target group code I can better describe the target that was photographed, I hope....