raster-package: Overview of the functions in the raster package

raster-packageR Documentation

Overview of the functions in the raster package


The raster package provides classes and functions to manipulate geographic (spatial) data in 'raster' format. Raster data divides space into cells (rectangles; pixels) of equal size (in units of the coordinate reference system). Such continuous spatial data are also referred to as 'grid' data, and be contrasted with discrete (object based) spatial data (points, lines, polygons).

The package should be particularly useful when using very large datasets that can not be loaded into the computer's memory. Functions will work correctly, because they process large files in chunks, i.e., they read, compute, and write blocks of data, without loading all values into memory at once.

Below is a list of some of the most important functions grouped by theme. See the vignette for more information and some examples (you can open it by running this command: vignette('Raster'))


The package implements classes for Raster data (see Raster-class) and supports

  • Creation of Raster* objects from scratch or from file

  • Handling extremely large raster files

  • Raster algebra and overlay functions

  • Distance, neighborhood (focal) and patch functions

  • Polygon, line and point to raster conversion

  • Model predictions

  • Summarizing raster values

  • Easy access to raster cell-values

  • Plotting (making maps)

  • Manipulation of raster extent, resolution and origin

  • Computation of row, column and cell numbers to coordinates and vice versa

  • Reading and writing various raster file types


I. Creating Raster* objects

RasterLayer, RasterStack, and RasterBrick objects are, as a group, referred to as Raster* objects. Raster* objects can be created, from scratch, files, or from objects of other classes, with the following functions:

raster To create a RasterLayer
stack To create a RasterStack (multiple layers)
brick To create a RasterBrick (multiple layers)
subset Select layers of a RasterStack/Brick
addLayer Add a layer to a Raster* object
dropLayer Remove a layer from a RasterStack or RasterBrick
unstack Create a list of RasterLayer objects from a RasterStack
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II. Changing the spatial extent and/or resolution of Raster* objects

merge Combine Raster* objects with different extents (but same origin and resolution)
mosaic Combine RasterLayers with different extents and a function for overlap areas
crop Select a geographic subset of a Raster* object
extend Enlarge a Raster* object
trim Trim a Raster* object by removing exterior rows and/or columns that only have NAs
aggregate Combine cells of a Raster* object to create larger cells
disaggregate Subdivide cells
resample Warp values to a Raster* object with a different origin or resolution
projectRaster project values to a raster with a different coordinate reference system
shift Move the location of Raster
flip Flip values horizontally or vertically
rotate Rotate values around the date-line (for lon/lat data)
t Transpose a Raster* object
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III. Raster algebra

Arith-methods Arith functions (+, -, *, ^, %%, %/%, /)
Math-methods Math functions like abs, sqrt, trunc, log, log10, exp, sin, round
Logic-methods Logic functions (!, &, |)
Summary-methods Summary functions (mean, max, min, range, prod, sum, any, all)
Compare-methods Compare functions (==, !=, >, <, <=, >=)
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IV. Cell based computation

calc Computations on a single Raster* object
overlay Computations on multiple RasterLayer objects
cover First layer covers second layer except where the first layer is NA
mask Use values from first Raster except where cells of the mask Raster are NA
cut Reclassify values using ranges
subs Reclassify values using an 'is-becomes' matrix
reclassify Reclassify using a 'from-to-becomes' matrix
init Initialize cells with new values
stackApply Computations on groups of layers in Raster* object
stackSelect Select cell values from different layers using an index RasterLayer
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V. Spatial contextual computation

distance Shortest distance to a cell that is not NA
gridDistance Distance when traversing grid cells that are not NA
distanceFromPoints Shortest distance to any point in a set of points
direction Direction (azimuth) to or from cells that are not NA
focal Focal (neighborhood; moving window) functions
localFun Local association (using neighborhoods) functions
boundaries Detection of boundaries (edges)
clump Find clumps (patches)
adjacent Identify cells that are adjacent to a set of cells on a raster
area Compute area of cells (for longitude/latitude data)
terrain Compute slope, aspect and other characteristics from elevation data
Moran Compute global or local Moran or Geary indices of spatial autocorrelation
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VI. Model predictions

predict Predict a non-spatial model to a RasterLayer
interpolate Predict a spatial model to a RasterLayer
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VII. Data type conversion

You can coerce Raster* objects to Spatial* objects using as, as in as(object, 'SpatialGridDataFrame')

raster RasterLayer from SpatialGrid*, image, or matrix objects
rasterize Rasterizing points, lines or polygons
rasterToPoints Create points from a RasterLayer
rasterToPolygons Create polygons from a RasterLayer
rasterToContour Contour lines from a RasterLayer
rasterFromXYZ RasterLayer from regularly spaced points
rasterFromCells RasterLayer from a Raster object and cell numbers
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VIII. Summarizing

cellStats Summarize a Raster cell values with a function
summary Summary of the values of a Raster* object (quartiles and mean)
freq Frequency table of Raster cell values
crosstab Cross-tabulate two Raster* objects
unique Get the unique values in a Raster* object
zonal Summarize a Raster* object by zones in a RasterLayer
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IX. Accessing values of Raster* object cells

Apart from the function listed below, you can also use indexing with [ for cell numbers, and [[ for row / column number combinations

getValues Get all cell values (fails with very large rasters), or a row of values (safer)
getValuesBlock Get values for a block (a rectangular area)
getValuesFocal Get focal values for one or more rows
as.matrix Get cell values as a matrix
as.array Get cell values as an array
extract Extract cell values from a Raster* object (e.g., by cell, coordinates, polygon)
sampleRandom Random sample
sampleRegular Regular sample
minValue Get the minimum value of the cells of a Raster* object (not always known)
maxValue Get the maximum value of the cells of a Raster* object (not always known)
setMinMax Compute the minimum and maximum value of a Raster* object if these are not known
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X. Plotting

See the rasterVis package for additional plotting methods for Raster* objects using methods from 'lattice' and other packages.

plot Plot a Raster* object. The main method to create a map
plotRGB Combine three layers (red, green, blue channels) into a single 'real color' image
spplot Plot a Raster* with the spplot function (sp package)
image Plot a Raster* with the image function
persp Perspective plot of a RasterLayer
contour Contour plot of a RasterLayer
filledContour Filled contour plot of a RasterLayer
text Plot the values of a RasterLayer on top of a map
Interacting with a map
zoom Zoom in to a part of a map
click Query values of Raster* or Spatial* objects by clicking on a map
select Select a geometric subset of a Raster* or Spatial* object
drawPoly Create a SpatialPolygons object by drawing it
drawLine Create a SpatialLines object by drawing it
drawExtent Create an Extent object by drawing it
Other plots
plot x-y scatter plot of the values of two RasterLayer objects
hist Histogram of Raster* object values
barplot barplot of a RasterLayer
density Density plot of Raster* object values
pairs Pairs plot for layers in a RasterStack or RasterBrick
boxplot Box plot of the values of one or multiple layers
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XI. Getting and setting Raster* dimensions

Basic parameters of existing Raster* objects can be obtained, and in most cases changed. If there are values associated with a RasterLayer object (either in memory or via a link to a file) these are lost when you change the number of columns or rows or the resolution. This is not the case when the extent is changed (as the number of columns and rows will not be affected). Similarly, with projection you can set the projection, but this does not transform the data (see projectRaster for that).

ncol The number of columns
nrow The number of rows
ncell The number of cells (can not be set directly, only via ncol or nrow)
res The resolution (x and y)
nlayers How many layers does the object have?
names Get or set the layer names
xres The x resolution (can be set with res)
yres The y resolution (can be set with res)
xmin The minimum x coordinate (or longitude)
xmax The maximum x coordinate (or longitude)
ymin The minimum y coordinate (or latitude)
ymax The maximum y coordinate (or latitude)
extent The extent (minimum and maximum x and y coordinates)
origin The origin of a Raster* object
crs The coordinate reference system (map projection)
isLonLat Test if an object has a longitude/latitude coordinate reference system
filename Filename to which a RasterLayer or RasterBrick is linked
bandnr layer (=band) of a multi-band file that this RasterLayer is linked to
nbands How many bands (layers) does the file associated with a RasterLayer object have?
compareRaster Compare the geometry of Raster* objects
NAvalue Get or set the NA value (for reading from a file)
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XII. Computing row, column, cell numbers and coordinates

Cell numbers start at 1 in the upper-left corner. They increase within rows, from left to right, and then row by row from top to bottom. Likewise, row numbers start at 1 at the top of the raster, and column numbers start at 1 at the left side of the raster.

xFromCol x-coordinates from column numbers
yFromRow y-coordinates from row numbers
xFromCell x-coordinates from row numbers
yFromCell y-coordinates from cell numbers
xyFromCell x and y coordinates from cell numbers
colFromX Column numbers from x-coordinates (or longitude)
rowFromY Row numbers from y-coordinates (or latitude)
rowColFromCell Row and column numbers from cell numbers
cellFromXY Cell numbers from x and y coordinates
cellFromRowCol Cell numbers from row and column numbers
cellsFromExtent Cell numbers from extent object
coordinates x and y coordinates for all cells
validCell Is this a valid cell number?
validCol Is this a valid column number?
validRow Is this a valid row number?
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XIII. Writing files

setValues Put new values in a Raster* object
writeRaster Write all values of Raster* object to disk
KML Save raster as KML file
blockSize Get suggested block size for reading and writing
writeStart Open a file for writing
writeValues Write some values
writeStop Close the file after writing
update Change the values of an existing file
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XIV. Manipulation of SpatialPolygons* and other vector type Spatial* objects

Some of these functions are in the sp package. The name in bold is the equivalent command in ArcGIS.

bind append combine Spatial* objects of the same (vector) type
erase or "-" erase parts of a SpatialPolygons* object
intersect or "*" intersect SpatialPolygons* objects
union or "+" union SpatialPolygons* objects
cover update and identity for a SpatialPolygons and another one
symdif symmetrical difference of two SpatialPolygons* objects
aggregate dissolve smaller polygons into larger ones
disaggregate explode: turn polygon parts into separate polygons (in the sp package)
crop clip a Spatial* object using a rectangle (Extent object)
select select - interactively select spatial features
click identify attributes by clicking on a map
merge Join table (in the sp package)
over spatial queries between Spatial* objects
extract spatial queries between Spatial* and Raster* objects
as.data.frame coerce coordinates of SpatialLines or SpatialPolygons into a data.frame
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XV. Extent objects

extent Create an extent object
intersect Intersect two extent objects
union Combine two extent objects
round round/floor/ceiling of the coordinates of an Extent object
alignExtent Align an extent with a Raster* object
drawExtent Create an Extent object by drawing it on top of a map (see plot)
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XVI. Miscellaneous

rasterOptions Show, set, save or get session options
getData Download and geographic data
pointDistance Distance between points
readIniFile Read a (windows) 'ini' file
hdr Write header file for a number of raster formats
trim Remove leading and trailing blanks from a character string
extension Get or set the extension of a filename
cv Coefficient of variation
modal Modal value
sampleInt Random sample of (possibly very large) range of integer values
showTmpFiles Show temporary files
removeTmpFiles Remove temporary files
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XVII. For programmers

canProcessInMemory Test whether a file can be created in memory
pbCreate Initialize a progress bar
pbStep Take a progress bar step
pbClose Close a progress bar
readStart Open file connections for efficient multi-chunk reading
readStop Close file connections
rasterTmpFile Get a name for a temporary file
inMemory Are the cell values in memory?
fromDisk Are the cell values read from a file?
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Extensive contributions were made by Jacob van Etten, Jonathan Greenberg, Matteo Mattiuzzi, and Michael Sumner. Significant help was also provided by Phil Heilman, Agustin Lobo, Oscar Perpinan Lamigueiro, Stefan Schlaffer, Jon Olav Skoien, Steven Mosher, and Kevin Ummel. Contributions were also made by Jochen Albrecht, Neil Best, Andrew Bevan, Roger Bivand, Isabelle Boulangeat, Lyndon Estes, Josh Gray, Tim Haering, Herry Herry, Paul Hiemstra, Ned Hornig, Mayeul Kauffmann, Bart Kranstauber, Rainer Krug, Alice Laborte, John Lewis, Lennon Li, Justin McGrath, Babak Naimi, Carsten Neumann, Joshua Perlman, Richard Plant, Edzer Pebesma, Etienne Racine, David Ramsey, Shaun Walbridge, Julian Zeidler and many others.


Except where indicated otherwise, the functions in this package were written by Robert J. Hijmans

raster documentation built on July 9, 2023, 6:12 p.m.