Where does the pattern on a tartan begin?

[Powermac]

So, odd question, and not kilt-related, but I figured if anyone knew the answer, it'd be you lot.

When looking at a tartan, where does the pattern begin? What bit can you boil it down to, small as possible, and say "that's (insert tartan here)"? Reason I ask is, I'm going to be getting a tattoo, and I want a bit of color. I want the color to call to mind the MacDonald tartan. I don't want to get the tartan tattooed on me...it's a bit busy, and I think my kilt's enough MacDonald tartan, but I want the colors to be the same, and vaguely in the same pattern, enough to suggest the tartan. I'm wondering if there's a certain section of the pattern I need to focus on, or if I can just grab a section that encompasses all the reds and blues and greens and call it a day.

Am I making any sense at all here?