There are two types of numeric scales. In all charts that use numeric scales, type:'linear' is the default, but it's not always the best option. A linear chart is best to compare data points of the same magnitude, but when the samples contain some values that are hundreds of times larger than others, data correlations may be hard to find.
A linear scale was used to for the following scatter chart, which plots the populations of several countries, comparing their population in 1980 (y axis) with their population in 2015 (x axis). The data is from the United Nations (see Data/WPP2017_UNH.csv in the GitHub repository for this chapter). The median line represents the points where the population is the same. Countries that appear in the shaded area above the middle line experienced a decrease in population:
A chart showing population increase/decrease from 1980 to 2015. Due to the different order of magnitude between China, India, and the rest of the world...