Using Card Maps are easier than you think. I found this one online:
I have a envelope filled with blank cardstock in an array of sizes. I used inexpensive cardstock and each piece of paper has the measurement written on them.
I begin with a blank canvas - THE CARD BASE. I pull out different sizes to see which fits best for the design.
The one I choose happened to be a proportional size, in other words the margins are 3/8" on all sides.
This is how I ended up with the finished card.
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BUT - Just because the card map shows a butterfly, doesn't mean you have to use a butterfly!