pdflscape
Great post, will surely help me with my next Latex project where I have a wide table I want to display. I also researched this problem and found it on stackexchange where it is solved in a similar way. -> Therefore the solution is certainly correct and will help some of us, thanks for sharing!
You can use the pdflscape package for this, which you must initialize in the following way:
\usepackage{pdflscape}
To then use it inside your document you must use the following commands:
\begin{landscape}
{your diagram}
\end{landscape}
Note that this can result in the page number being misplaced if you include one. For this you can copy the following definition to your code and then add the \placepagenumber comand above the \end{landscape} comand:
\def\placepagenumber{%
\par\pagestyle{empty}%
\vbox to 0pt{\vss}\vfill
\vbox to 0pt{\baselineskip0pt
\hbox to\linewidth{\hss}%
\baselineskip\footskip
\hbox to\linewidth{%
\hfil\thepage\hfil}\vss}}
