Equidistant set
Set of points equidistant from two sets
In mathematics, an equidistant set (also called a midset, or a bisector) is a set whose elements have the same distance (measured using some appropriate distance function) from two or more sets. The equidistant set of two singleton sets in the Euclidean plane is the perpendicular bisector of the segment joining the two sets. The conic sections can also be realized as equidistant sets. This property of conics has been used to generalize the notion of conic sections. The concept of equidistant set is used to define frontiers in territorial domain controversies. For instance, the United Nations Convention on the Law of the Sea (Article 15) establishes that, in absence of any previous agreement, the delimitation of the territorial sea between countries occurs exactly on the median line every point of which is equidistant of the nearest points to each country. Though the usage of the terminology is quite old, the study of the properties of equidistant sets as mathematical objects was initiated only in 1970's.
01Definition
Let (X, d) be a metric space and A be a nonempty subset of X. If x is a point of X, the distance of x from A is defined as d(x, A) = inf{ d(x, a): a in A}. If A and B are both nonempty subsets of X then the equidistant set determined by A and B is defined to be the set {x in X: d(x, A) = d(x, B)}. This equidistant set is denoted by { A = B }.
The study of equidistant sets is more interesting in the case when the background metric space is the Euclidean space.
02Examples
Straight lines
Conics as equidistant sets
Sources and credits
This article is adapted from the Wikipedia article “Equidistant set”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Equidistant-set-of-two-singleton-sets-in-a-plane.gif by Krishnachandranvn, CC BY-SA 3.0
- Equidistant-set-of-two-straight-lines.png by Krishnachandranvn, CC BY-SA 3.0
- Equidistant-set-of-a-singleton-set-and-a-straight-line.gif by Krishnachandranvn, CC BY-SA 3.0
- Equidistant-set-of-two-circles-ellipse.gif by Krishnachandranvn, CC BY-SA 3.0
- Equidistant-set-of-two-circles-hyperbola.gif by Krishnachandranvn, CC BY-SA 3.0
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