Vegetation Classification and Mapping Project Report - USGS

USGS-NPS Vegetation Mapping Program
Colonial National Historical Park
Data from 183 accuracy assessment points were entered into an Excel spreadsheet listing
accuracy assessment point ID, vegetation map polygon ID, vegetation map class, and first and
second (if available) map class determination from accuracy assessment field observations. The
thematic accuracy of the vegetation map was then tabulated using a contingency matrix that
compares the map class observed on the ground (accuracy assessment observation) with the map
class mapped at the same location on the final vegetation map (reference data). The contingency
table lists reference data values in the columns and accuracy assessment observation values in
the rows. The number of each reference data and accuracy assessment observation pair for all
sampling locations is indicated at each row/column intersection in the matrix. Correct mappings
are indicated on the table where the row and column values are the same and typically occur on
the diagonal on the matrix. Overall percent accuracy and Kappa index were calculated for the
map using equations from the USGS-NPS VMP accuracy assessment guidelines (The Nature
Conservancy and Environmental Systems Research Institute 1994c). Overall percent accuracy
was calculated by dividing the number of correctly classified accuracy assessment points by the
total number of accuracy assessment points. The Kappa index is the preferred method of
reporting overall thematic accuracy because it takes into account that a certain number of correct
classifications will occur by chance (Foody 1992). The USGS-NPS VMP protocol requires that
the Kappa index of vegetation maps exceed 80% (The Nature Conservancy and Environmental
Systems Research Institute 1994c). To calculate the probability that a reference data observation
has been correctly classified (producer’s accuracy or omission error), the number of reference
data points correctly classified is divided by the total number of reference data points in that map
class. To calculate the probability that the mapped vegetation classes represent the vegetation
actually found on the ground (user’s accuracy or commission error), the number of correctly
classified reference samples was divided by the total number of samples classified or mapped to
that vegetation class. The errors of omission and errors of commission for mapped vegetation
classes should exceed 80%, according to the USGS-NPS VMP protocol (The Nature
Conservancy and Environmental Systems Research Institute 1994c).
Metadata Preparation
All map products are accompanied by detailed Federal Geographic Data Committee (FGDC)
compliant metadata (FGDC 1998a). Metadata are data about data. They describe the content,
quality, condition, and other characteristics of the data. Metadata are critical elements of each
spatial dataset, allowing future users of the data to understand how the dataset was developed, its
appropriate uses, and to locate specific information within the spatial dataset. Metadata records
were prepared for each mosaic, for the vegetation map, and for the all georeferenced plot data
and accuracy assessment point data.
A metadata record for each set of mosaics was prepared in accordance with the current Federal
Geographic Data Committee standards (FGDC 1998a). Metadata were produced in notepad and
parsed using the USGS metadata compiler (USGS 2004). After all errors and omissions
identified by the parser were corrected, the metadata compiler was used to generate final TXT,
HTML, and XML versions of each metadata record which are stored in the data archive. Key
information for the leaf-on (fall) and leaf-off (spring) mosaics and for the formation-level
vegetation dataset is summarized in Tables 8 and 9, respectively.
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