\documentclass[12pt]{standalone} \usepackage{ucs} \usepackage[utf8x]{inputenc} \usepackage[T1]{fontenc} \usepackage{textcomp} \renewcommand{\rmdefault}{ugm} \renewcommand{\sfdefault}{phv} \usepackage[garamond]{mathdesign} \usepackage{tikz} \usetikzlibrary{positioning, shapes, arrows, shadows} \begin{document} \tikzset{ observed/.style={circle, draw}, partly observed/.style 2 args={draw, fill=#2, path picture={ \fill[#1, sharp corners] (path picture bounding box.south west) -| (path picture bounding box.north east) -- cycle;}, circle}, unobserved/.style={draw, circle, fill=gray!40}, residual/.style={draw, rectangle} } \tikzset{>=latex} \begin{tikzpicture} \matrix [draw, below, font=\small, align=center, column sep=2\pgflinewidth, inner sep=0.4em, outer sep=0em, nodes={align=center, anchor=center}] at (current bounding box.south){ \node[observed,label=right:observed] {}; \\ \node[unobserved,label=right:automatically classified]{}; \\ \node[residual,label=right:error term]{}; \\ }; \end{tikzpicture} \end{document}