How to find the nearest point in the coordinate system There are so many points in the coordinate system. When a specific point is given in the coordinate system, I want to find the closest point to the straight line distance. For example, if you have 800 points, calculate the distance 800 times and find the smallest value. But I want to make more efficient algorithm that doesn't execute 800 times due to that it might be sorted in a certain order before searching.
That is, if the points is put in a certain order, 
 Could you recommend some notions?
So, if I understand correctly, you have a set $S$ of points in some space (do you have a specific dimension ?), and a point $x$, and you want to find the point of $S$ that is the closest to $x$ ? 

If this is indeed what you are trying to do, have a look at K-d trees and Voronoï tesselation. These methods are based on space partitioning to make queries faster.