On peut modifier `x=...` et `y=...` :
\documentclass[french,a4paper]{scrartcl}
%\documentclass[french,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ttscale=0.82]{libertine}
\usepackage{tikz}
\usepackage{babel}
\begin{document}
\begin{tikzpicture}[x=0.1pt,y=0.1pt]
\begin{tikzpicture}[x=0.030cm,y=0.030cm]
\coordinate (top) at (0,650);
\coordinate (bottom) at (7.5,0);
\draw (top) -- (bottom);
\end{tikzpicture}
\end{document}
