what is the cylindrical coordinate system?
what is the cylindrical coordinate system? This system helps to analyze the geometry of a coaxial cable and we can analyze its electric field intensity or electric field more easily using them. Three coordinates that are used for representing a point in cylindrical are P(р,Ф,Ζ). р is the radial distance of a cylindrical surface, Ф is the angle that a point makes with the x-axis in counter clockwise direction, z is the height of a cylinder. These three coordinates give us constant planes. At top surface of the cylinder, z is constant while р andФ are variables. Similarly at outer cylindrical surface, р is constant while Ф and Ζ are variable. The cross sectional plane obtained by cutting the cylinder vertically gives us a plane on which Ф is constant while р and Ζ vary.
The following picture shows how these cylindrical coordinate systems with their unit vectors are represented.

video lecture of cylindrical coordinate systems
https://www.youtube.com/watch?v=h-oy0lklXHk
Also read here
https://eevibes.com/electromagnetic-field-theory/what-is-the-cartesian-coordinate-system/