# Why do we start measuring angle from positive direction of X axis only?

Why do measure the angle from positive X axis in coordinate geometry? Further we also say clockwise rotation would produce negative angles? How can angles be negative? I mean, how much is $-30°$? Does that even make sense?

There is no particular reason we measure positive angles as counterclockwise from the positive $x$ axis, it was adopted as a convention in order to standardize the way we do it. Negative angles are also used in the way you ask, as a clockwise rotation.
In the Argand diagram, $e^{it}$ is a point on the unit circle when $t$ is real. It lies on the positive $x$-axis for $t=0$, and when $t$ increases it moves anti-clockwise about the unit circle, and when $t$ decreases it moves clockwise. This is the reason that in complex analysis, anti-clockwise is regarded as the positive direction.
It is clear that in the plane, we rotate in at most two possible directions, from some initial configuration. If we wish to describe all such rotations in such a way that we want the original configuration to be identified with the real number $0$ (and we do want this for reasons I've explained elsewhere), then it is clear that all rotations in one direction would be positive while the oppositely directed rotations would be negative (whichever is which is our choice to make).