Scatter Diagram: Graphical Representation for two Quantitative Variables
A scatterplot (also called a scatter graph or scatter Diagram) is used to observe the strength and direction between two quantitative variables. In statistics, the quantitative variables follow the interval or ratio scale from measurement scales.
Usually, in scatter, diagram the independent variable (also called the explanatory, regressor, or predictor variable) is taken on the X-axis (the horizontal axis) while on the Y-axis (the vertical axis) the dependent (also called outcome variable) is taken to measure the strength and direction of the relationship between the variables. However, it is not necessary to take explanatory variables on X-axis and outcome variables on Y-axis. Because, scatter diagram and Pearson’s correlation measure the mutual correlation (interdependencies) between the variables, not the dependence or cause and effect.
Diagram below describe some possible relationship between two quantitative variables (X & Y). A short description is also given on each possible relationship.
For more about correlation see the post link below