4-color chart

Quick answer：

A 4-color chart, also known as a four-color map, is a type of thematic map that uses four colors to represent different data categories. It is widely used in cartography and data visualization to represent various geographic or statistical information. The concept is based on the four-color theorem, which states that any map can be colored using no more than four colors in such a way that no two adjacent areas have the same color.