8.3 Reclass Toolset

library(raster)
library(arc2r)
library(dplyr)

8.3.1 Reclassify

In GIS quite often arises the necessity to reclassify a raster dataset. In other words, to create new classes with different range of values for the existing cell values of the dataset. This operation in ArcGIS Pro is performed using the Reclassify (Spatial Analyst) tool. In R the respective operation is quite straightforward and is based on the use of the reclassify function of the raster package. For our example we use the raster dataset swissAlti3D.

data("swissAlti3D")

plot(swissAlti3D)

Let’s have a look at the histogram of the raster values to see their distribution.

histinfo <- hist(swissAlti3D)

The histogram above automatically created 13 breaks (620,640,…,840,860). We can use these breaks to reclassify our values. To do so, we create below a reclassification matrix with the respective values.

# create a reclassification matrix
reclass_vec <- histinfo$breaks

reclass_m <- matrix(c(lag(reclass_vec, default = 0), reclass_vec, seq_along(reclass_vec)), 
    ncol = 3)


reclass_m

##       [,1] [,2] [,3]
##  [1,]    0  620    1
##  [2,]  620  640    2
##  [3,]  640  660    3
##  [4,]  660  680    4
##  [5,]  680  700    5
##  [6,]  700  720    6
##  [7,]  720  740    7
##  [8,]  740  760    8
##  [9,]  760  780    9
## [10,]  780  800   10
## [11,]  800  820   11
## [12,]  820  840   12
## [13,]  840  860   13

After creating the respective matrix with the new classes, we are ready to call the reclassify function. The function takes as a first argument the dataset set to be reclassified and as second the matrix, on which the reclassification is based on.

swissAlti3D_reclass <- reclassify(swissAlti3D, reclass_m)

plot(swissAlti3D_reclass)

Figure 8.1: Aspect of swissALTI3D2019 in 4 classes