Change default width of images in graphicx package

Some options of package graphicx can be set using \setkeys:

\documentclass{article}
\usepackage{graphicx}
\setkeys{Gin}{width=\linewidth}

\begin{document}
  \noindent
  \includegraphics{test1}
\end{document}

What is Gin ? Documentation:

Here ‘Gin’ is the name used for the keyval keys associated with ‘Graphics inclusion`.