Example of a Lorenz curve for Wikipedia: https://commons.wikimedia.org/wiki/File:Lorenz-Kurve_Beispiel.svg

Lorenz-Kurve.tex

% Lorenz curve

% by n.st, originally created on 2014-02-08

% based on
% - http://www.texample.net/tikz/examples/line-plot-example/
% - http://tex.stackexchange.com/a/51766

\documentclass[crop,tikz,convert={outext=.svg,command=\unexpanded{pdf2svg \infile\space\outfile}},multi=false]{standalone}
\usepackage[utf8]{inputenc}

\begin{document}
\begin{tikzpicture}[y=.1cm, x=.1cm]
    \path[fill=white] (-25,-25) rectangle (115,115);

    %axes
    \draw (0,0) -- coordinate (x axis mid) (100,0);
    \draw (0,0) -- coordinate (y axis mid) (0,100);
    \draw[help lines] (100,0) -- (100,100);
    \draw[help lines] (0,100) -- (100,100);

    %ticks
    \foreach \x in {0,20,...,100}
        \draw (\x,1pt) -- (\x,-3pt)
            node[anchor=north] {\x\%};
    \foreach \y in {0,20,...,100}
        \draw (1pt,\y) -- (-3pt,\y) 
            node[anchor=east] {\y\%}; 

    %labels
    \node[below=0.8cm] at (x axis mid) {\% der Bevölkerung};
    \node[rotate=90, above=0.8cm] at (y axis mid) {\% des Einkommens};

    %lines
    \draw[ultra thick,domain=0:100,smooth,variable=\x] plot ({\x},{\x});

    \newcommand*{\CenterOffset}{40}
    \draw[ultra thick] (100,100) arc
        (
            -asin(\CenterOffset/(100+\CenterOffset)) :
            -acos(\CenterOffset/(100+\CenterOffset)) :
            148 % = approx. sqrt((102+\CenterOffset)^2 + (2+\CenterOffset)^2)
        );

    \renewcommand*{\CenterOffset}{0}
    \draw[ultra thick,dashed] (100,100) arc
        (
            -asin(\CenterOffset/(100+\CenterOffset)) :
            -acos(\CenterOffset/(100+\CenterOffset)) :
            100 % = approx. sqrt((100+\CenterOffset)^2 + \CenterOffset^2)
        );

    \draw[ultra thick,->] (64,36) -- (70,30);

\end{tikzpicture}
\end{document}