In arc2r/book: All things R Spatial or A guide to spatial R for Recovering ArcGIS Users

Surface Toolset

Slope and Aspect

In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incl.
Source: "http://wiki.gis.com/wiki/index.php/Slope"

In GIS and specifically in terrain analysis, calculating the terrain slope is of great importance, since it can play a significant role in various forms of technical analysis. The most common way of calculating the slope is from a Digital Elevation Model (DEM).

In ArcGIS pro the tool used for computing the slope of a raster dataset with elevation data is called Slope (3D Analyst).It identifies the steepness at each cell of a raster surface. The lower the slope value, the flatter the terrain; the higher the slope value, the steeper the terrain.

In R, raster package includes the function terrain(), which helps us compute slope, aspect and other terrain characteristics from a raster with elevation data.
Let's start by computing the slope of the swissAlti3d raster dataset.

data("swissAlti3D")

plot(swissAlti3D)

After importing and visualizing our raster dataset, we use the terrain function to calculate the slope.

# Computing the slope of a raster dataset using the terrain() function
swissAlti3d_slope <- terrain(swissAlti3D, opt="slope", unit="degrees")
plot(swissAlti3d_slope)

In the function above, we define the operation we want to perform as the second argument of the function (opt = "slope"). Furthermore, we also define the units of the final result.
Similarly, we compute the aspect of a given dataset. Basically as aspect we can consider the compass direction that a slope leans towards.
Let's compute now, using again the same function terrain, the aspect of the same dataset swissALTI3D2019.

# Computing the aspect of the terrain dataset
swissAlti3d_aspect <- terrain(swissAlti3D, opt="aspect", unit="degrees")
plot(swissAlti3d_aspect)

So, R gives us the option to retrieve multiple terrain characteristics of a raster dataset, using only one function. The aforementioned spatial operation in ArcGIS pro could be performed using the tool Aspect (Spatial Analyst).

arc2r/book documentation built on March 5, 2021, 2:10 p.m.