Create a named vector with levels and colour values
Add commment to script
Modify indentation of script
Open loop to process 'file_list' CSV files
Read in a CSV file from the 'file_list' vector object
Determine the number of receptors in the x and y directions
Get the UTM coordinate extents for both x and y
Bind the x and extents into a matrix
Create a PROJ.4 string for the UTM zone
Create a SpatialPoints object for the bbox in UTM coords
Apply spatial transform to reproject the UTM coords into lat/lon
Create a matrix object that is a bounding box in lat/lon
Create a SpatialPoints object in UTM for all x and y vals
Apply spatial transform to reproject UTM x and y vals to lat/lon
Extract data frame from SpatialPixels lat/lon coords object
Bind concentration values to df with lat/lon receptor coords
Create a simplified set of column names for data frame
Cut 'conc' column in df into named factor levels
Get map tile from Stamen Maps
Create a named vector with levels and colour values