A Contour Plot is a visualisation method used to represent a 3D plotted surface onto a 2D graph. It displays the relationship and changes between two independent variables (X and Y) and a dependent variable (Z).

On a Contour Plot, the X and Y variables are plotted on the horizontal and vertical axes, while the Z variable is represented by contour lines or coloured bands. Tightly spaced contour lines indicate rapid changes in the Z variable, while widely spaced lines suggest that the changes are gradual.

Contour Plots allow for the easy identification of maxima, minima, and optimal combinations of X and Y variables that produce desired Z values. In general, Contour Plots are useful when you need to understand the relationship between three variables simultaneously or identify combinations of two variables that produce specific outcomes in a third variable.

Tools to generate a Contour Plot with:
Observable Plot (JS)
Plotly (Chart Studio and Excel) + Python version
Python: bokeh – matplotlb – seaborn
R / ggplot
Stata