The vertical distance of a point from origin in two dimensional space is called the ordinate. It is also called as the $y$-coordinate.
The ordinate is a geometric coordinate of a point, which is helpful to know how far the point is from origin in vertical direction in Bi-dimensional rectangular Cartesian coordinate system.
It is measured from origin in vertical direction by comparing the number line on the $y$-axis. Hence, the ordinate is also called as the $y$-coordinate of the point.
The $x$-axis is considered as base line while measuring the ordinate or $y$-coordinate of a point because the $x$-axis is passed through the origin in two dimensional Cartesian coordinate system.
Here, $Q$ is a point on the plane and the vertical distance of the point is measured as $d$ units from origin by taking $x$-axis as base line and also comparing it with the number line on $y$-axis.
Therefore, the vertical distance $d$ is called the ordinate or $y$-coordinate of the point $Q$.
There are two basic steps to find the ordinate of any point in geometry.
Let’s learn how to measure the ordinate or $y$-coordinate of any point from the following understandable example.
Let $P$, $Q$, $R$ and $S$ be four points in a two dimensional rectangular Cartesian coordinate system. Now, use the above two steps to determine the $y$-coordinate of every point.
Do not forget that the number line on the $y$-axis is considered while measuring the $y$-coordinate. So, it is not required to look at the number line on the $x$-axis.
Thus, the ordinate or $y$-coordinate of every point can be determined geometrically.
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