The elevated planet in a chart should occupy the Tenth House, or Ninth. It should be close to the Midheaven (I generally call a planet "elevated" when it is anywhere in the 10th, or within 15 degrees of the MC in the 9th. I take a rather flexible approach in this, but that is the general rule I follow.
The elevated planet is that planet closest to the MC. The MC is the highest point a planet can reach in the sky. In the 10th House it is still ascending, thus gaining in power. In the 9th House it is descending and waning in power.
There is a second classification called "most elevated planet." The planet does not meet the criteria above and so is not "elevated." But among all other planets it is the highest in the sky. This is not a dignity as in true "elevation." But it does give a certain additional power and importance to the planet.
Another use of elevation is when comparing two planets, usually two in aspect. That one which is higher in the sky tends to be dominant over the one lower. Other things such as dignity/debility, whether sign occupied is commanding/obedient, direct/retrograde, etc. also influence this judgment of relative power.
But the dignity of "elevated planet" should be reserved to a planet in the 10th or 9th House, and proximity to the MC is definitely a factor. If a planet is thus elevated, we can say that "it stands above all else."
My MC is at 27 Pisces. Mercury, in the 8th and near the 9th cusp is at 24 Aquarius. The arc distance is 33 degrees. This means that Mercury does not qualify as "elevated," but no other planet is closer to the MC, so Mercury is the "most elevated planet." This condition is not a dignity, but does enter into judgment of relative strength compared to another planet in aspect to Mercury.
Mercury is square Saturn at 22 Taurus. Saturn is then at 55 degrees from the MC. So Mercury, being more elevated, is granted dominance over Saturn on that basis. But Mercury is in the sign of Saturn (Aquarius) and rulership outweighs this type of elevation. Saturn disposes Mercury and is therefore the more powerful of the two. Also Saturn is in the east and ascending, while Mercury is west and descending. Also, in judging this relative power, it is important to note which of the two planets is applying, which separating. And other factors enter into the equation.