In this recipe, we will learn how to make contour plots to visualize topographical data, such as the terrain near a mountain or a volcano.
We are only using the base graphics functions for this recipe. So, just open up the R prompt and type the following code. We will use the inbuilt volcano
dataset, so we need not load anything.
Let's first make a default contour plot with volcano
:
contour(x=10*1:nrow(volcano), y=10*1:ncol(volcano), z=volcano, xlab="Metres West",ylab="Metres North", main="Topography of Maunga Whau Volcano")
We used the contour()
base graphics library function to make the graph.
The x
and y
arguments specify the locations of the grid at which the height values (z
) are specified. The volcano dataset contains topographic information on a 10 x 10 m grid, so we set the x
and y
grid arguments to 10 times the index numbers of rows and columns, respectively.
The contour data, z
, is provided by the volcano dataset in a...