Accuracy Assessment: Shiloh National Military Park (SHIL)

Smart, L.; Smyth, R.; White, R.

This report presents the accuracy assessment for the digital vegetation map of Shiloh National Military Park (SHIL). Vegetation at SHIL was mapped by The University of Georgia Center for Remote Sensing and Mapping Science (Jordan and Madden 2010) with ecological consultation and assistance from NatureServe. The mapping was conducted as part of the National Park Service Vegetation Mapping Program. The map accuracy was assessed by comparing mapped vegetation types to field verified vegetation types at randomized evaluation points. The evaluation points were chosen prior to field work using statistical methods to ensure full representation of the range of map classes in the park. Accuracy was calculated for each individual map class and for all map classes combined. The accuracy assessment process is not intended to exclusively judge the performance of the mapper or the ecologists on the project since error can be caused at any point during the mapping and accuracy assessment process. Remotely-sensed imagery is limited in its ability to differentiate between certain forest types and even the most experienced mappers cannot differentiate between certain species of oaks or pines in a remotely sensed image. Sources of error for the mapping project are varied and include more than solely "remote sensing error" but also include "ecologist error" caused by poor interpretation of the vegetation community concept, "field worker error" caused by mistakes made by fieldworkers while collecting the data (including misreading of the key), and temporal error when conditions on the ground change between the mapping and assessment processes. It is difficult to isolate a single error that is causing accuracy issues without more research. The accuracy assessment, therefore, should be used more as a tool to discern usability of map classes rather than a way to judge the performance of the mapmakers. The University of Georgia (UGA) Team focused on generating the highest level of detail possible during park vegetation mapping to provide the most accurate information for the National Park Service. As a consequence, assessment of the finished project requires a two step approach: (1) assessing the overall accuracy of the finest-scale map produced, and (2) combining the most "confused" map classes to determine the accuracy measures at coarser scales. The report provides the best approximation of individual map class accuracy and also suggests combinations of map classes to produce a more reliable map at a coarser scale. For SHIL, the overall accuracy of the final map, which includes eleven map classes (nine grouped map classes and two singular map classes), is 78.8%, with a kappa statistic of 0.58 (58%). This version of the map is the most appropriate for use by the standard user; what it misses in fine-scale detail, it makes up for in the relatively high level of accuracy of map classes.

Accuracy Assessment: Shiloh National Military Park (SHIL)

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