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If we go with Scorp's idea, then for the second and subsequent visits, it should be 1.5 points, otherwise the difference between 1 and 2 or more visits is too large. And without any visits, it should be 0.3.
2. Stinger: New people are not prohibited from coming, but we want those who will actually come to choose the city.
We could also introduce a system of contributions. If you are a virtual participant and want to become a real one, then make a deposit, for example, 1,000, and your vote will be worth a maximum of 1.5 points. If the city wins, the money will go towards paying for your accommodation; if it doesn't win, the money will be returned. If a virtual participant doesn't show up, the money goes into the organizers' fund to cover initial expenses, such as renting a conference hall.
The important thing is to gather as many people as possible.