Through 2004, all comprehensive maps of science had to use the databases from ISI (Institute for Scientific Information, now Thomson Reuters). These databases covered a broad base of the scientific literature, but only a very small fraction of the technical literature. Growth in the ISI citation databases through 2004 remained focused on the scientific literature, as shown above.
The discontinuity shown above at 2004 is due to the appearance of Scopus, the first competitor to ISI. Scopus indexed far more technical documents (such as conference papers) than did ISI, and had greater overall coverage per year. We used both databases for a time, and have used Scopus exclusively since 2006. Over the years these vendors have responded to each other in a competitive sense by adding content. Scopus still indexes more current content than Thomson; however, original source material in the Thomson database goes back much further in time.
We are the first research group to generate an integrated global map from two very large databases – Scopus and US patents. However, as represented above, there is still a very long way to go before full coverage of the scientific and technical literature can be achieved. Many additional databases exist, containing tens of millions of additional documents. We will be obtaining and adding additional databases over the next few years so that we obtain a more global representation of worldwide S&T activity.