Columbia subject headings:
Maps.
Welsh language--History--20th century--Maps.
Welsh language--History--20th century--Statistics.
Welsh language--History--20th century.
Harvard subject headings:
Linguistic atlases.
Wales--Population--Maps.
Welsh language--20th century--History.
Welsh language--20th century--Maps.
Welsh language--20th century--Statistics.
Welsh language--20th century.
Welsh language--Maps.
Welsh language--Statistics.
Princeton subject headings:
Welsh language--20th century--History.
Welsh language--20th century--Maps.
Welsh language--20th century--Statistics.