Icon size for sports pitch icons

Hello all,

I am thinking of making some icons for a sports pitches sport:cricket and sport:bowls.

I notice that the icon on the wiki for sport-soccer.png is 45 by 55 pixels

and the icon for sport-swimming is 38 by 38 pixels

Is there a link anywhere for guidelines to shape, size, colour or theme for icons, I also assume that the icons should be submited for approval as SVG files and PNG’s

Thanks in advance