Collectors of Clason state road maps issued between 1923 and 1931 are presented with challenges around determining map publication dates. Unlike Rand McNally and Gousha, the Clason Map Company typically did not place dates or date codes on its products during this period. A systematic review of the maps contained in Clason state road maps, touring atlases, and Green Guides reveal that the road legends and other map symbols varied over the years in systematic ways. This Clason Map website, with content developed by Mark Greaves and Carl Liedholm, represents an attempt at providing a guide to dating these maps. The Guide is proudly hosted online by the MSU Map Library.