This guidance is a revision and update of the 1994 guidance on thematic accuracy assessment for the NPS Vegetation Inventory (Environmental Systems Research Institute et al. 1994). The revision incorporates the sampling design and analysis principles described by the 1994 version as a sound starting framework and by augments them with practical experience gained by the NPS and its cooperators and contractors at more than 100 NPS parks over 15 years. NPS staff informally interviewed many individuals in and outside the NPS who have been involved in project production and oversight. We evaluated specifically thematic accuracy assessment practices in the field and in analysis at more than 30 NPS parks. As a result, this guidance is designed to be scientifically sound, but also practical to implement. While it specifically addresses NPS objectives, it may also be found useful as guidance for other organizations that assess the accuracy of vegetation maps.