replaced overlay() with lapp() function in objective section

Author: dafnidrake

episodes/04-raster-calculations-in-r.Rmd

@@ -12,7 +12,7 @@ source("setup.R")
 ::::::::::::::::::::::::::::::::::::::: objectives
 
 - Perform a subtraction between two rasters using raster math.
-- Perform a more efficient subtraction between two rasters using the raster `overlay()` function.
+- Perform a more efficient subtraction between two rasters using the raster `lapp()` function.
 - Export raster data as a GeoTIFF file.
 
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