I think that it is important to point out when they say “citation map,” they’re talking about not just the ability to look backwards at what articles a paper has cited. They’re also talking about the ability to see what articles cited the article that you are looking at. This requires that the citation data from those later articles be structured enough to be consistently be linked to the article that they are citing. This can be more difficult that it looks when we consider different style manuals, transcription errors, different naming conventions (Given or family name listed first), title abbreviations (does J. Phys. mean Journal of physics or journale de physique)
It is also worth remembering just how hard West Publishing tried to claim copyright in the CITATIONS to public domain works.
