Vegetation Classification and Mapping Project Report - USGS

Vegetation Classification and Distribution Mapping Report: Petrified Forest National Park
Table 11. Terminology used for accuracy assessment data collection and analysis at Petrified Forest National Park.
Terminology
Reference map class
Sample map class
Contingency table or
error matrix
Users accuracy
Producers accuracy
Overall accuracy
Kappa Index
Definition
Map class observed in the field during accuracy assessment, considered to be the true map class.
Map class assigned in the vegetation map database.
A matrix where rows indicate the sample map classes and columns represent the reference map classes. At
each row and column intersection, the number of observations for each sample/reference combination is
noted. The vegetation map database is considered correct for all the cases where the sample map class and
the reference map class are the same. These observations usually occur on the diagonal on the matrix.
The number of correct reference observations divided by the total number of reference observations for a
map class.
The number of sample map classes correctly mapped divided by the total number of reference observations
made for that map class.
The total number of correctly classified reference observations divided by the total number of reference
observations regardless of map class.
An alternate expression of overall accuracy with correction for chance correct classifications.
targeted for accuracy assessment, such as
a land-cover class observed as a reference
observation but not targeted as a sample,
were not included in the calculation of
the kappa index. Statistics were derived
using the JMP v5.1 statistical application.
The two-tailed, 90% confidence intervals
for users, producers and overall accuracy
were calculated using Score Confidence
Interval Tables, which have better coverage
probabilities with smaller sample, sizes
(Agresti and Coull 1998).
4.1.4 Group, Macrogroup, and Management
Map Classes
After assessment statistics were calculated
for the base map classes, the SBSC team
developed three aggregated map-class
schemas: the group, macrogroup, and
management map schemas. The group
map-class schema is an aggregation of
base map classes based on the concept
of the group level of the NVCS Version
2 (Federal Geographic Data Committee
2008) (see table 2). The SBSC team used
the ecological-system assignments for
associations developed by NatureServe
as a substitute for assignment of group
map class, which were not available
in final form at the time this project
was completed. The macrogroup is an
additional midlevel grouping in the NVCS
Version 2, one level of aggregation above
the group.
Management map classes reflect base
map-class performance and resource
management needs. User and producer
accuracy statistics for each map class, as
well as confusion among map classes as
shown on the base map contingency table
(see Appendix H1), were used to develop
recommendations for aggregations of
commonly confused and floristically or
ecologically similar map classes. PEFO
resource management staff reviewed these
map-class recommendations at a meeting
held at the park on May 17, 2007. They
made recommendations for management
class aggregations using management
goals for particular plant communities
of particular interest, regardless of their
assessed accuracy performance.
The SBSC team created a cross-walk
between the base map classes and each
aggregated map class (see Appendix F).
The crosswalks were used to add the
group, macrogroup, and management map
classes to the map database. The team also
created a crosswalk between the reference
data for the accuracy assessment and the
group, macrogroup, and management map
classes to conduct an accuracy assessment
of each aggregated map class. The number
of polygons and the area of each map class
within the base, group, macrogroup, and
management map-class schemas were
calculated within a GIS.
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