AFAIK all registered users can vote for the mapcycle every week. The map with most votes goes at the top of the cycle and so on. Maps with least votes don't get into the cycle at all. There are a big cycle (for when many players are connected) and the small cycle (for when few players are connected). Look for the "map cycle" link next to the red flashing light at the top of the page.
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If the light turns green, you have already voted that week.
P.S.: If you're wondering how come every other map is kingdom or crossing, that's because in-game nextmap votes/commands reset the cycle.