Use complete sentences to describe how measurements of position in two directions (vertical and horizontal) are sufficient enough to describe the position of an object on a flat surface. ? ?

A flat surface has only two dimensions,width and height, which in mathematical terms can be expressed as horizontal (x) and vertical (y) values.  With only the x and y coordinates you can locate a point in any part of a plane (flat surface).  These coordinates are expressed in pairs of numbers separated by a comma, like (3,2) where the first number is the x-coordinate and the second number is the y-coordinate.