Cartesian coordinates are the rectilinear x,y (2D) or x,y,z (3D) cooridinates we see in graphs and maps. These are a common way to represent locations on a plane or in space, or pixels in an image, but sometimes alternatives are used, for example, ((radial coordinates}} where (in 2D) each point. is represented as a distance and angle from centre point. Soemtimes a change in representation can make mathematical analysis or machine learning easier.
Used on Chap. 7: page 132