Fixing the Font Issue in Venn Diagrams with Tikz Latex

Question

I am novice when it comes to Tikz. I have three Venn Diagrams. Fore some reason the text inside the Venn diagrams start at the lower half of the node. Is there a way to automatically align/fit it to the size of the shape?

\def\firstcircle{(0,0) circle (2.1cm)}
\def\secondcircle{(55:3.5cm) circle (2.1cm)}
\def\thirdcircle{(0:3.5cm) circle (2.1cm)}
\centering
\begin{tikzpicture}[>=stealth,on grid,auto] 
\begin{scope}[shift={(4cm,-15cm)}, fill opacity=0.5]
        \fill[gray!30!white] \firstcircle;
        \fill[blue!30!white] \secondcircle;
        \fill[cyan!60!white] \thirdcircle;
        \draw \firstcircle node[below] {
        \begin{tabular}{c}
        \textbf{Economic Layer}: \\
        A\\
        B\\
        C\\
        D
        \end{tabular}
        };
        \draw \secondcircle node [above,text width=2cm,align=center] {
         \begin{tabular}{c}
         \textbf{Technology Layer}\\
         A \& B\\
         C \& D
         \end{tabular}
         };
        \draw \thirdcircle node [below,text width=2cm,align=center] {
        \begin{tabular}{c}
        \textbf{Social  Layer}\\
        A\\
        B\\
        C
        \end{tabular}
        };
    \end{scope}
\end{tikzpicture}   

Answer 1

If you want the text in the centre then you can add the text centered option to the tikz picture.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes, positioning}

\begin{document}
\def\firstcircle{(0,0) circle (2.1cm)}
\def\secondcircle{(55:3.5cm) circle (2.1cm)}
\def\thirdcircle{(0:3.5cm) circle (2.1cm)}

\centering
\begin{tikzpicture}[>=stealth,on grid,auto, text centered] 
\begin{scope}[shift={(4cm,-15cm)}, fill opacity=0.5]
        \fill[gray!30!white] \firstcircle;
        \fill[blue!30!white] \secondcircle;
        \fill[cyan!60!white] \thirdcircle;
        \draw \firstcircle node[] {
        \begin{tabular}{c}
        \textbf{Economic Layer}: \\
        A\\
        B\\
        C\\
        D
        \end{tabular}
        };
        \draw \secondcircle node [] {
         \begin{tabular}{c}
         \textbf{Technology Layer}\\
         A \& B\\
         C \& D
         \end{tabular}
         };
        \draw \thirdcircle node [] {
        \begin{tabular}{c}
        \textbf{Social  Layer}\\
        A\\
        B\\
        C
        \end{tabular}
        };
    \end{scope}
\end{tikzpicture}   

\end{document}

By my eye there is still a problem with this though as the bottom left circle labeled "economic layer" overlaps slightly. To fix this manually you could use the xshift and yshiftoptions for each node to fine tune the positioning.

Answer 2

Probably you still don't know, but nodes can have different shapes. The basic ones are rectangular and circular but you can find come more in shapes tikzlibrary.

In your code, circles and text are different entities and you have to adjust them. Another solution could be to use circular nodes:

\node[draw, circle, minimum size=4.2cm, fill=gray!30, align=center, opacity=0.5, text opacity=1] 
    {\\
    \textbf{Economic Layer}: \\
    A\\
    B\\
    C\\
    D
    };

This command draws a circle with minimum radius=2.1cm (if inner text needs more space, the node will grow) and text aligned to center. By declaring align option, there's no need to include tabulars inside the node but \\ is still valid as newline command.

Instead of repeating all these options in every node, you can declare a .style:

mycircle/.style={draw, circle, minimum size=4.2cm, align=center, 
                  fill=#1, opacity=0.5, text opacity=1}

This style has one parameter (#1) which corresponds to filling color.

Your code could be written like:

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[mycircle/.style={draw, circle, minimum size=4.2cm, align=center, 
                    fill=#1, opacity=0.5, text opacity=1}] 
        \node[mycircle=gray!30] {\\
        \textbf{Economic Layer}: \\
        A\\
        B\\
        C\\
        D
        };
        \node[mycircle=blue!30] at (60:3.5cm) {
         \textbf{Technology Layer}\\
         A \& B\\
         C \& D
         };
        \node[mycircle=cyan!60] at (0:3.5cm) {
        \textbf{Social  Layer}\\
        A\\
        B\\
        C
        };
\end{tikzpicture}   
\end{document}