It's obvious how the designers did this. You start with your position in the middle of the graph. You are given a question that will move you to the right a corresponding number of spaces depending on how strongly you agree with it. Then you are given an opposite question that will move you to the left depending on how strongly you agree with it. Ditto for up and for down.
If you check the same answer for the left question and the right question, they balance each other out, and your position on the graph lands right in the centre.
If you do that for all of the questions, your final position is smack dab in the centre of the graph, and that happens to be closest to the Liberal Party position.
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