A Global Map of Science Based on the ISI Subject Categories

TL;DR

This paper constructs a comprehensive global map of scientific disciplines using ISI subject categories and citation data, revealing the structure and interdisciplinary relations within science.

Contribution

It introduces a method to visualize the disciplinary structure of science through factor analysis of citation data and maps these relations at multiple levels of aggregation.

Findings

Identified 14 main scientific disciplines.

Mapped interdisciplinary relations, especially in nanoscience.

Provided online interactive maps of science structure.

Abstract

The ISI subject categories classify journals included in the Science Citation Index (SCI). The aggregated journal-journal citation matrix contained in the Journal Citation Reports can be aggregated on the basis of these categories. This leads to an asymmetrical transaction matrix (citing versus cited) which is much more densely populated than the underlying matrix at the journal level. Exploratory factor analysis leads us to opt for a fourteen-factor solution. This solution can easily be interpreted as the disciplinary structure of science. The nested maps of science (corresponding to 14 factors, 172 categories, and 6,164 journals) are brought online at http://www.leydesdorff.net/map06/index.htm. An analysis of interdisciplinary relations is pursued at three levels of aggregation using the newly added ISI subject category of "Nanoscience & nanotechnology". The journal level provides the finer grained perspective. Errors in the attribution of journals to the ISI subject categories are averaged out so that the factor analysis can reveal the main structures. The mapping of science can, therefore, be comprehensive at the level of ISI subject categories.