Sections from MD from A B to C and DE (Drafts)  Visualizing
Functions: An Overview References 
Linear
Functions (LF) Quadratic Functions(QF) 
GeoGebra (online)  "Mapping Diagrams Visualizing Functions and Equation Solutions: From Algebra Basics to Real and Complex Analysis." (GeoGebra Book)  "Linear Algebra & Mapping Diagrams: Old & New Visualizations" (GeoGebra Book) 
YouTube Videos 
Using Mapping Diagrams to Visualize Linear Functions (10 Minutes)Solving Linear Equations Visualized with Mapping Diagrams.

14th International Congress on Mathematical Education, "MAPPING DIAGRAMS: FUNCTION VISUALIZATION OF REAL AND COMPLEX ANALYSIS AND MATRIX ALGEBRA", Shanghai, July 14, 2021. Topic Study Group 23 Visualization in the teaching and learning of mathematics (GeoGebra Book includes Paper)
(On YouTube) Using Mapping Diagrams to Understand Functions 