stehman2014 {mapaccuracy}

Thematic map accuracy and area under stratified random sampling when the strata differ from the map classes.

Description

Implements the estimators described in Stehman (2014) for overall accuracy, producer's accuracy, user's accuracy, and area. Includes precision estimates.

Usage

stehman2014(s, r, m, Nh_strata, margins = TRUE, order)

Arguments

s

character vector. Strata class labels. The object will be coerced to factor.

r

character vector. Reference class labels. The object will be coerced to factor.

m

character vector. Map class labels. The object will be coerced to factor.

Nh_strata

numeric vector. Number of pixels forming each stratum. It must be named (see details).

margins

logical. If FALSE, the error matrix produced includes no margins (sum of the rows and columns).

order

(optional) character vector. Classes to be displayed in the results and their sequence. If missing, equal to sort(unique(c(r,m))).

Details

Argument Nh_strata must be named to explicitly and clearly identify the stratum that each entry refers to. The names of Nh_strata are expected to match the strata class labels of argument s.

In the error matrix returned, the entries corresponding to no observed cases will present NA rather than 0. This is to emphasize the difference between the absence of cases and the presence of some (few) cases that represent a very small proportion of area (almost zero) and thus possibly rounded to zero. However, NA means zero proportion of area.

Value

A list with the estimates and error matrix.

OA

overall accuracy

UA

user's accuracy

PA

producer's accuracy

area

area proportion

SEoa

standard error of OA

SEua

standard error of UA

SEpa

standard error of PA

SEa

standard error of area proportion

matrix

confusion error (area proportion). Rows and columns represent map and reference class labels, respectively

Author(s)

Hugo Costa

References

Stehman, S. V. (2014). Estimating area and map accuracy for stratified random sampling when the strata are different from the map classes. Int. J. Remote Sens., 35, 4923-4939.

Examples

# Numerical example in Stheman (2014)
s<-c(rep("A",10), rep("B",10), rep("C",10), rep("D",10))
m<-c(rep("A",7), rep("B",3), "A", rep("B",11), rep("C",6), "B", "B", rep("D",10))
r<-c(rep("A",5), "C", "B", "A", "B", "C", "A", rep("B",5), "A", "A", "B", 
     "B", rep("C",5), "D", "D", "B", "B", "A", rep("D",7), "C", "C", "B")
Nh_strata<-c(40000, 30000, 20000, 10000)
names(Nh_strata)<-c("A", "B", "C", "D")
e<-stehman2014(s, r, m, Nh_strata)

e$area[1]                  # Proportion of area of class A (compare with paper in p. 4932)
e$area[3]                  # Proportion of area of class C (p. 4932)
e$OA                       # Overall accuracy (p. 4932)
e$UA[2]                    # User's accuracy of class B (compare with paper in p. 4934)
e$PA[2]                    # Producer's accuracy of class B (p. 4934)
e$matrix[2,3]              # Cell (2, 3) of the error matrix (p. 4935)
e$SEa[1]                   # Standard error (SE) for proportion of area of class A (p. 4935)
e$SEa[3]                   # Standard error (SE) for proportion of area of class C (p. 4935)
e$SEoa                     # SE for overall accuracy (p. 4936)
e$SEua[2]                  # SE for user's accuracy of class B (p. 4936)
e$SEpa[2]                  # SE for producer's accuracy of class B (p. 4936)

# change class order
stehman2014(s, r, m, Nh_strata, order=c("D","C","B","A"))

# the number (and name) of strata and map classes may differ
s<-c(rep("a",5), rep("aa",5), rep("b",10), rep("c",10), rep("d",10))
Nh_strata<-c("a"=20000, "aa"=20000, "b"=30000, "c"=20000, "d"=10000)
stehman2014(s, r, m, Nh_strata)

# m (map) may include classes not found in r (reference)
m<-c(rep("A",7), rep("B",3), "A", rep("B",11), rep("C",6), "B", "B", rep("D",9), "XX")
stehman2014(s, r, m, Nh_strata)

# r (reference) may include classes not found in m (map)
m<-c(rep("A",7), rep("B",3), "A", rep("B",11), rep("C",6), "B", "B", rep("D",10))
r<-c(rep("A",5), "C", "B", "A", "B", "C", "A", rep("B",5), "A", "A", "B",
     "B", rep("C",5), "D", "D", "B", "B", "A", rep("D",7), "C", "C", "YY")
stehman2014(s, r, m, Nh_strata)

# can add classes not found neither in r nor m
stehman2014(s, r, m, Nh_strata, order=c("A","B","C","D","YY","ZZ"))