Intro to Raster Data in R
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The GeoTIFF file format includes metadata about the raster data.
To plot raster data with the ggplot2 package, we need to convert it to a dataframe.
R stores CRS information in the Proj4 format.
Be careful when dealing with missing or bad data values.
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Plot Raster Data in R
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Continuous data ranges can be grouped into categories using mutate() and cut() .
Use built-in terrain.colors() or set your preferred color scheme manually.
Layer rasters on top of one another by using the alpha aesthetic.
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Reproject Raster Data in R
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In order to plot two raster data sets together, they must be in the same CRS.
Use the projectRaster() function to convert between CRSs.
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Raster Calculations in R
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Rasters can be computed on using mathematical functions.
The overlay() function provides an efficient way to do raster math.
The writeRaster() function can be used to write raster data to a file.
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Work With Multi-Band Rasters in R
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A single raster file can contain multiple bands or layers.
Use the stack() function to load all bands in a multi-layer raster file into R.
Individual bands within a stack can be accessed, analyzed, and visualized using the same functions as single bands.
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Open and Plot Shapefiles in R
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Shapefile metadata include geometry type, CRS, and extent.
Load spatial objects into R with the st_read() function.
Spatial objects can be plotted directly with ggplot using the geom_sf() function. No need to convert to a dataframe.
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Explore and Plot by Shapefile Attributes
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Spatial objects in sf are similar to standard data frames and can be manipulated using the same functions.
Almost any feature of a plot can be customized using the various functions and options in the ggplot2 package.
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Plot Multiple Shapefiles in R
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Use the + operator to add multiple layers to a ggplot.
Multi-layered plots can combine raster and vector datasets.
Use the show.legend argument to set legend symbol types.
Use the scale_fill_manual() function to set legend colors.
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Handling Spatial Projection & CRS in R
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Convert from .csv to a Shapefile in R
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Know the projection (if any) of your point data prior to converting to a spatial object.
Convert a data frame to an sf object using the st_as_sf() function.
Export an sf object as text using the st_write() function.
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Manipulate Raster Data in R
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Use the crop() function to crop a raster object.
Use the extract() function to extract pixels from a raster object that fall within a particular extent boundary.
Use the extent() function to define an extent.
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Raster Time Series Data in R
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Use the list.files() function to get a list of filenames matching a specific pattern.
Use the facet_wrap() function to create multi-paneled plots with ggplot2 .
Use the as.Date() function to convert data to date format.
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Create Publication-quality Graphics
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Use the theme_void() function for a clean background to your plot.
Use the element_text() function to adjust text size, font, and position.
Use the brewer.pal() function to create a custom color palette.
Use the gsub() function to do pattern matching and replacement in text.
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Derive Values from Raster Time Series
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Use the cellStats() function to calculate summary statistics for cells in a raster object.
The pipe (| ) operator means or .
Use the rbind() function to combine data frames that have the same column names.
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