Building the soilclass dataframe

1 Introduction

Generalized map of soil phosphorus retention potential

In this 2011 ISRIC map we can distinguish 16 different main classes of map unit according to its soil phosphorus retention potential.

library(soilP)     # Phosphorus maps

2 Where did soilclass data came from?

See the manual for details.

?soilclass

2.1 Extracting palette from Arcgis P_retention_class_main layer.

This operation was carried out in ArcGis on the mxd file. I just copied to the corresponding soilclass column r,g,b, the RGB values from the legend of the unique values symbology in the layer P_retention_class_main properties.

data_dir    <- system.file("data",    package = "soilP", mustWork = TRUE)
extdata_dir <- system.file("extdata", package = "soilP", mustWork = TRUE)
soilclass <- read.csv(file.path(extdata_dir,"P_retention_class.csv")) 
soilclass

2.2 Adding hexadecimal strings and R standard names to colors.

color_hex <- apply(soilclass %>% dplyr::select(r,g,b), 
                   1, 
                   function(x){rgb(x[1], x[2], x[3],
                                   maxColorValue = 255)
                   })
color_name <- sapply(sapply(color_hex, plotrix::color.id), 
                       `[[`, 
                       1) # extracts first of multiple possible names
  
soilclass$color_hex <- color_hex
soilclass$color_name <- color_name
soilclass

2.3 Reordering according to ascending Phosphorus Retention Potential.

This is step is critical for rendering color legend in the right way (reproducing arcgis appearance of the generalized map).

The ascending column integers were manually assigned. For the Low map unit main class, higher percentage of Low soil unit P retention corresponded to lower integers. For the Moderate, High, and very High map unit main classes, higher integers were assigned to higher percentage of corresponding soil unit P retention. This means the higher the Low soil unit P retention percentage the lower the integer, and complentarily the higher the Moderate, High, and Very High soil unit P retention percentage the higher the integer. This assignation is naive and consequently both, intuitive and ad hoc.

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TODO: We should establish a data based order of map unit soil phosphorus retention classes instead of postulating an ad hoc order. This can be done through selecting the first discriminant dimension from a Discriminant Analysis of the percentage of soil unit phosphorus retention classes per mapping unit. Furthermore, we can use that discriminant dimention as a continuous variable instead of the discrete classes for downstream analyses.

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soilclass <- soilclass[order(soilclass$ascending),]
save(soilclass, file = file.path(data_dir,"soilclass.RData"))
soilclass