The map uses a complex scheme, with colors differentiating language families (“Teutonic”, “Romanic” &c) and patterns differentiating individual languages within each family. Superimposed on these are dashed red lines indicating political boundaries as they had stood in 1914 and solid red lines showing the much-changed boundaries of 1924. The latter were largely the result of the Paris Peace Conference of 1919-1920, at which the victorious Allies dictated the terms of peace to the defeated Central Powers, and in so doing rearranged the maps of Europe and the Near East. I cannot comment much on the accuracy of Jastrow’s treatment of languages, though for what it’s worth I stumbled on a Wikipedia entry describing the hypothesis of a “Ural-Altaic” family of languages as controversial (As an aside, see here for an interesting persuasive map making hay out of the Ural-Altaic hypothesis.)
The first edition of the map was copyrighted in December 1919, during the Paris Peace Conference. One driver of the Conference was the push for national self-determination, that is, for greater political autonomy and sovereignty for ethnic, linguistic, and cultural groups within Europe and beyond. I have not yet found documentary evidence that this particular map was used at the Paris Conference, but the timing is certainly suggestive.
As the map shows, the push for national self-determination led to the breakup of the multi-national empires controlled by the Central Powers, in particular the Austro-Hungarian and the Ottoman Empires, and to the creation (or re-creation) of nation-states such as Austria, Hungary, Czechoslovakia and Poland. In at least some cases, such as Austria, Hungary, Lithuania and Romania, new national boundaries correspond rather nicely to the linguistic boundaries delineated by Jastrow. However, as also indicated by this map, what it did not lead to, at least in the short term, was the breakup of empires controlled by the victorious allied powers of Great Britain, France and Italy. That would come later, as a result of the Second World War and the work of nationalist movements in Africa and Asia.
Morris Jastrow, Jr.
Born in Warsaw in 1861, Jastrow moved with his family to Philadelphia in 1866 after his father, a renowned Talmud scholar, accepted a rabbinical position. After graduating from the University of Pennsylvania in 1881, he studied theology and semitic languages at a number of European institutions before returning to the United States in 1885. Rather than pursuing the rabbinate, however, he accepted a position at his alma mater as an instructor, later full professor, of Semitic languages and dedicated his career to archaeological, linguistic and Biblical studies, and to the study of Near Eastern religions in general. In 1888 he also took a position as a librarian at the University and was promoted to librarian-in-chief a decade later. He achieved considerable repute in his field, serving as President of the American Oriental Society (1914-15) and the Society of Biblical Literature (1916), and after his death in 1921 was honored by a long appreciation in the Journal of the American Oriental Society. As this second edition of the map was published in or around 1924, after Jastrow’s death, it is not clear who acted as editor.
Given his obviously deep but I imagine relatively narrow expertise in Semitic languages, it strikes me as odd that Rand McNally would have selected Jastrow as editor for this map, though perhaps he was assisted by a team of linguists whom for whatever reason are not credited. What is clear is that national self-determination was a topic very much on Jastrow’s mind at the time: In 1920 he published The Eastern Question and Its Solution (Philadelphia and London: J.B. Lippincott Company), where he argued for cooperation by the victors of the First World War in advancing the cause independence for the peoples of the Near East.
OCLC #41291355 (Buffalo & Erie County Public Library, Columbia, Cornell, Ave Maria University, University of Chicago, Cleveland Public Library). OCLC #1225946728 gives an example at the Staatsbibliothek zu Berlin, dating it (likely incorrectly) to 1923. Harvard and the Newberry Library’s Rand McNally Collection also hold examples of this edition. OCLC #1088724183 and 80321204 give examples of the 1919 edition at Syracuse, the Milwaukee County Library, and the Univ. of Wisconsin-Milwaukee.