I am taking a beginner course in machine learning and have confused myself horribly about something. The idea is that there is a line which splits a 2D plane into two distinct regions as shown in the figure:
Now the instructor says that anything below the line is greater than $0$ and anything above is less than $0$. Now, it is not clear to me why that should be? Is there an intuition behind why anything below this line should be greater than zero (according to the line equation) and anything above should be less than 0.