shape default size

[vwf <vwf vulkor net>]

Hello,

I made my own shape that works fine. The shape is '10' wide, but
10-what? When I put a shape on the canvas it is about 2.5 screen units, 
but the A4 seems about 15 wide. 

For normal use I would like to see the shape/image larger; now I always
resize the shape to make them fit arrowheads and texts. I tried
increasing the size in the shape file to 30 but this seemed to have no
effect.

How do I set the default size of a shape?

Now I'm on the topic: how do I set all defaults: e.g. linewidth,
arrowheads, font, fontsize, png export-resolution?

Thanks,
Frits