How to make (1,1) mean (1cm,1cm) in TikZ? (Setting the units of coordinates)

I have a picture in TikZ and I'd like to change the basic units of the coordinates I specify. I know I could just scale the picture, but I don't want to do that. For any given coordinate, I can write (1cm,1cm) etc for each coordinate, but I'd rather specify the "units" I want to use separately... Or for example make (1,1) mean (5ex,10ex)...

Is there a way to do this?

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See my answer, you can use x=..., y=.... and it's possible to use macro to adjust x=\myx, y=\myy –  Alain Matthes Jun 6 '11 at 15:11

By default yes but you can compare the next results

\begin{tikzpicture}
\draw(0,0)--(1,1);
\end{tikzpicture}

\begin{tikzpicture}[x=2cm,y=-1cm]
\draw(0,0)--(1,1);
\end{tikzpicture}

\begin{tikzpicture}[x=5,y=5]
\draw(0,0)--(1,1);
\end{tikzpicture}

\begin{tikzpicture}[x=28.45274,y=28.45274]
\draw(0,0)--(1,1);
\end{tikzpicture}


In the last code, we can see that without unit x and yare defined with pt

\begin{tikzpicture}
\draw (0,0)--(600,0);
\end{tikzpicture}


Latex Error: ... Dimension too large. The unit is the cm.

\begin{tikzpicture}[x=0.01 cm]
\draw (0,0)--(600 cm,0);
\end{tikzpicture}


again Latex Error: ... Dimension too large because 600 cm is a length and TeX uses only lengths < 575 cm.

\begin{tikzpicture}[x=0.01 cm]
\draw (0,0)--(600,0);
\end{tikzpicture}


This is correct ! 600 < $2^{31}-1$ . 600 is a integer and not a length and now 600 gives 6 cm

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I see, I was trying to be too clever: I was trying things like [canvas cs:x=1cm,y=cm] but that gave me errors. I didn't think to just try x=... Thanks! –  Seamus Jun 6 '11 at 18:55