I have a path I’ve created in Illustrator and saved as an SVG.
Now I want to programmatically place it at different sizes and coordinates on a large canvas.
Say I’ve got this image:

(source: omgtldr.com)
How would I reproduce that same image in different places and sizes in one SVG file, like this:

(source: omgtldr.com)
for example, one version shrunk by 20% at coordinates x,y; another enlarged by 30% at coordinates a,b and so on.
Please assume I’m going to be OK with the programming part, I’m comfortable working with XML files. It’s the SVG parts I don’t understand.
You need the transform attribute. You can move your paths with translate and resize them with scale.