Mapping Science - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 308

Fig. 8.24 A similarity map of JCR journals shown in VOSViewer

The Butterfly designed by Jock Mackinlay and his colleagues at Xerox shows
both ends in the same view, but the focus is at the individual paper level rather than
at a macroscopic level of thousands of journals (Mackinlay et al. 1995 ). Eugene
Garfield's HistCite depicts direct citations in the literature. However, as the number
of citations increase, the network tends to become cluttered, which is a common
problem to network representations.
We introduce a dual-map overlay design that depicts both the citing overlay
and the cited overlay maps in the same view. The dual-map overlay has several
advantages over a single overlay map. First, it represents a citation instance
completely. One can see where it is originated and where it points to at a glance.
Second, it makes it easy to compare patterns of citations made by distinct groups of
authors, for example, authors from different organizations, or authors from the same
organization at different points of time. Third, it opens up more research questions
that can be addressed in new ways of analysis. For example, it becomes possible
to study the interdisciplinarity at both source and target sides. It becomes possible
to track the movements of scientific frontiers in terms of their footprints in both
base maps.
The construction of a dual-map base shares the initial steps but differs in later
steps. Once the coordinates are available for both citing and cited matrices of
journals, a dual-map overlay can be constructed. It is not necessary to have cluster
information, but additional functions are possible if cluster information is available.
In the rest of the description, we assume that at least one set of clusters are available