Dewey Decimal Charts and Graphs for archivebooks
The numbers are from the Dewey Decimal System® (DDC®). The wordings are from the Melvil Decimal System (MDS), which is like Dewey but not under copyright.
The MDS Spectrum is a representation of a library based on the distribution of books within MDS classes. Each color represents a set of books within a top-level class. MDS, The Melville Decimal System, is a free version of OCLC's Dewey Decimal System®.