The data was collected by The Vermont Agency of Natural Resources.  Barbara Burns, Southern Vermont's Forest health Specialist did the setchmapping and processing of the data.     Sketchmapping is a remote sensing technique of observing forest change events from an aircraft and documenting them manually onto a map.  It is considered both an art form and a form of scientific data collection, and is highly subjective.  The observer views a particular forest change event or damaged area on the forest. and delineates the affected area onto a map to record its size, shape, and location as accurately as possible.  Attributes, such as host, causal agent, symptom, and an estimate of intensityor number of trees affected, are also recorded.     Aerial sketch-map surveys have been recognized for over fifty years as an efficient and economical method of detecting and monitoring forest change events over large forested areas.  Since it is a relatively low cost method, it is relied upon to provide a course, landscape-level overview of forest health conditions.  If the forest change events discovered during the overview survey are considered high priority, it can be used as the first step of a multitiered process of detection, monitoring, and evaluation, using other remote sensing and ground sampling techniques.  No remotely sensed data is reliable without some amount of ground-truthing for tree species, causal agent and location.