I used data from the Ordnance Survey for some maps I created. License information for the Ordnance Survey says to cite OS data like this:

Contains Ordnance Survey data © Crown copyright and database right [year]

and can be found at this link: www.ordnancesurvey.co.uk/opendata/licence

I'm glad to use this citation, but I edited the data I downloaded a bit. What's in my maps differs from what I actually received from the OS. Should I say in the citation that the geospatial data is derived from data received from the Ordnance Survey? If you don't have an authoritative answer, I also welcome thoughtful responses. Thank you.