Graph Properties / Features

Let's look at features that graphs or digraphs have before viewing some special types of graphs.

1. In a directed edge $(v_1, v_2)$:
   • The node $v_1$ is called the initial vertex (or source vertex), and
   • The node $v_2$ is called the terminal vertex (or destination vertex).
   The direction of the edge goes from the initial vertex to the terminal vertex.
   

   The directed edge is $(\color{red}{1},\color{blue}{2})$. Vertex $\color{red} 1$ is the initial vertex, and vertex $\color{blue} 2$ is the terminal vertex. Miriam Briskman, CC BY-NC 4.0.

   \documentclass[border=1pt]{standalone}
   \usepackage{tikz}
   \usetikzlibrary{arrows.meta}
   
   \tikzset{
   vertex/.style={draw, circle, very thick, minimum size=1cm},
   edge/.style={very thick, -Triangle}
   }
   
   \begin{document}
   
   \begin{tikzpicture}
   
   \node[vertex, dotted, red] (v1) at (0,0) {1};
   \node[vertex, dashed, blue] (v2) at (4,0) {2};
   
   \draw[edge] (v1) -- (v2);
   
   \end{tikzpicture}
   
   \end{document}