Line chart (also called bar chart) is a kind of chart used to represent data, which is usually used to compare numerical values between different categories. Usually, it is not used to express the number of conditions in mathematical problems, but to express the information such as the number, size or proportion of data. For example, if you want to compare the population of different cities, you can use line charts to display the population of each city, so as to intuitively compare the size relationship between them.