Abstract
A defense of the Koppen system is supported by a new map which corrects Koppen''s for N. America by using new and fuller data and a larger scale. Certain modifications are introduced, but in the main the new map shows that Thornthwaite''s boundaries are little better than Koppen''s and not so simple to compute. Agreement with soil and vegetation boundaries is improved by the modifications and new data. Limits of "year climates" from Kendall''s and Russell''s studies are included on the map. The revision of the C/D boundary is shown to apply well to China and Europe. A very important contribution for biogeographers. The map is also available in folio (17 X 22 in.) form as No. 27 of "Climatic Maps of North America" by C. F. Brooks et al., Harvard U. Press.

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