What is the contour interval?

C. I or contour interval,

Explanation:

This line is represented by isopleth, isohaline, isohyets, isobars, and isorhythm, etc. Iso means equal. It is a function of variables of x and y on a plane surface. In cartography a contour line is drawn on a map to show various densities of relief feature, their spacing is indicated by these lines. Used to create a 3 dimensional model of the earth on a plain sheet of paper. Like Isopleths which are used to show precipitation, and the map drawn to show this is a choropleth map. Similarly, the Isobars are used to show a pressure difference on the map. The contour interval can range from 200m to 400m to 600m an so on.