\begin{tikzpicture}[x=1cm,y=1cm,font=\small,>=Latex,
 original/.style={circle,fill=black,inner sep=1.8pt},
 level/.style={circle,draw,fill=white,minimum size=6mm,inner sep=1pt},
 landmark/.style={circle,fill=orange!85!black,inner sep=2.5pt}]
\node at (3,4.35) {(a) \(L=12,\ q=1,\ t=4\)};
\node[original,label=left:\(0\)] (o) at (0,1.8) {};
\node[original,label=above left:\(1\)] (i) at (2.5,3.6) {};
\node[original,label=below left:\(2\)] (j) at (2.5,0) {};
\node[original,label=right:\(k\)] (k) at (6,1.8) {};
\draw[black!50] (o)--(i)--(k)--(j)--(o);
\draw[black!35,dashed] (o)--(k) node[pos=.42,above=3pt,text=black] {\(12\)};
\draw[blue!80!black,line width=2.4pt] (.85,2.412)--(1.21,2.6712);
\draw[blue!80!black,line width=2.4pt] (.85,1.188)--(1.21,.9288);
\node at (1.02,2.99) {\(e\)};
\node at (1.02,.61) {\(f\)};
\node at (0,2.55) {\(q=1\)};
\node at (0,1.05) {\(q=1\)};
\node[landmark] (x) at (3.6667,3) {};
\node[landmark] (y) at (3.6667,.6) {};
\node[above right=1pt] at (x) {\(x_{1k}(4)\)};
\node[below right=1pt] at (y) {\(x_{2k}(4)\)};
\node at (3.02,3.67) {\(4\)};
\node at (3.02,-.07) {\(4\)};
\node at (3.75,2.5) {\((14,17)\)};
\node at (3.75,1.1) {\((17,14)\)};
\node at (3,-.78) {The ordered pairs give distances to \((e,f)\).};
\node at (10.55,4.35) {(b) From positions to pairs of levels};
\foreach \n/\x/\y in {11/7.3/3.2,14/8.6/3.2,17/9.9/3.2,18/11.2/3.2,15/12.5/3.2,12/13.8/3.2,13/8.6/1.5,16/9.9/1.5,19/11.2/1.5}
  \node[level] (v\n) at (\x,\y) {\(\n\)};
\foreach \a/\b/\t in {11/14/1,17/18/7,15/18/5,12/15/2,13/16/3,16/19/6}
  \draw[->] (v\a)--(v\b) node[midway,above=4pt,font=\scriptsize] {\(t=\t\)};
\draw[->,orange!85!black,very thick] (v14)--(v17)
  node[midway,above=4pt,font=\scriptsize,text=black] {\(t=4\)};
\node at (10.55,.1) {Arrow \(t\) joins the distances at position \(t\).};
\node at (10.55,-.55) {Seven distinct pairs, no cycle.};
\end{tikzpicture}