Shanto Roy

I Explore Research, Tech, Travel, and Business. SRE @Charles Schwab.

4 minute read

While writing a paper, we often require to draw classification tree diagrams. In this post, I show you how to draw one in Latex. Previously, I used to draw one using draw.io. However, Latex is more convenient in terms of font size management.

You can also find the code and output in the Overleaf Document.

Include Packages

At first, include the tikz package:

\usepackage{tikz}

Then include the following libraries:

\usetikzlibrary{trees,positioning,shapes,shadows,arrows}

Set Basic Styles

Set basic node styles for different levels. Adjust the text width based on your diagram. Use thick instead of thin if wanted a thicker line for the nodes. I usually avoid colors; if you want to fill the nodes with colors, change the color from white to your desired one.

\tikzset{
  basic/.style  = {draw, text width=2cm, drop shadow, font=\sffamily, rectangle},
  root/.style   = {basic, rounded corners=2pt, thin, align=center, fill=white},
  level-2/.style = {basic, rounded corners=6pt, thin,align=center, fill=white, text width=3cm},
  level-3/.style = {basic, thin, align=center, fill=white, text width=1.8cm}
}

Final Code

Within the level 1 style definition, you can skip edge from parent path={(\tikzparentnode.south) -- (\tikzchildnode.north)} because it works the similar way by default. You can also omit edge from parent fork down if you want a straight arrow from root to level 1 children. Configure node distance according to your need.

\begin{figure}
    \centering
\begin{tikzpicture}[
  level 1/.style={sibling distance=12em, level distance=5em},
%   {edge from parent fork down},
  edge from parent/.style={->,solid,black,thick,draw}, 
  edge from parent path={(\tikzparentnode.south) -- (\tikzchildnode.north)},
  >=latex, node distance=1.2cm, edge from parent fork down]

% define root %
\node[root] {\textbf{Taxonomy}}

% Level-1 children %
  child {node[level-2] (c1) {\textbf{Category 1}}}
  child {node[level-2] (c2) {\textbf{Category 2}}}
  child {node[level-2] (c3) {\textbf{Category 3}}}
  child {node[level-2] (c4) {\textbf{Category 4}}};

% For Category 1 children %
\begin{scope}[every node/.style={level-3}]
\node [below of = c1, xshift=10pt] (c11) {item 1-1};
\node [below of = c11] (c12) {item 1-2};
\node [below of = c12] (c13) {item 1-3};

% For Category 2 children %
\node [below of = c2, xshift=10pt] (c21) {item 2-1};
\node [below of = c21] (c22) {item 2-2};
\node [below of = c22] (c23) {item 2-3};
\node [below of = c23] (c24) {item 2-4};

% For Category 3 children %
\node [below of = c3, xshift=10pt] (c31) {item 3-1};
\node [below of = c31] (c32) {item 3-2};
\node [below of = c32] (c33) {item 3-3};
\node [below of = c33] (c34) {item 3-4};
\node [below of = c34] (c35) {item 3-5};

% For Category 4 children %
\node [below of = c4, xshift=10pt] (c41) {item 4-1};
\node [below of = c41] (c42) {item 4-2};
\end{scope}


% Draw arrows from level-1 to it's children %
\foreach \value in {1,2,3}
  \draw[->] (c1.195) |- (c1\value.west);

\foreach \value in {1,...,4}
  \draw[->] (c2.195) |- (c2\value.west);
  
\foreach \value in {1,...,5}
  \draw[->] (c3.195) |- (c3\value.west);
  
\foreach \value in {1,2}
  \draw[->] (c4.195) |- (c4\value.west);
\end{tikzpicture}
    \caption{This is a simple Taxonomy}
    \label{fig:my_label}
\end{figure}

Output

The output looks like the following. Once again, you can also find the code and output in the Overleaf Document.

That’s all folks. Cheers!!! :smiley:

References

  1. edge from parent (dashed) makes nodes themselves dashed?
  2. Trees Examples
  3. TikZ and pgf

You can find a comprehensive list of Latex resources in the following post:

Latex Resources in a Nutshell

If you are a new Latex user, check out this post: 20 Most Common Mistakes Made by New Latex Users

You can find all Latex oriented posts of mine in: https://shantoroy.com/categories/#latex

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