I am trying to reproduce this diagram
So far I have tried
\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}[%
node distance=1.5cm,
filled/.style={circle,fill=red,text=white,minimum size=2cm}
]
\node [filled,label=below:{Primary Optical Area}] (1) {1};
\node [right=2cm of 1,filled,label=below:{Strong Fallow Area}] (2) {2};
\node [below=2cm of 1,filled,label=below:{Weak Fallow Area}] (3) {3};
\node [right=2cm of 3,filled,label=below:{Terminal Area}] (4) {4};
\end{tikzpicture}
\end{document}
which results in
which is not quite what I want.
How do I make the coordinate system, so it is equivalent with the first picture?


