Doubts in Quiver Plot

Can someone please explain what the quiver plot represents. I am confused after reading the lines " the arrow size represents magnitude of gradient" and The direction and slope of the arrow reflects the ratio of βˆ‚J(w,b)βˆ‚w and βˆ‚π½(𝑀,𝑏)βˆ‚π‘ at that point.
This is in reference to Course 1, Week 1, Lab 4 Gradient Descent Solution

That’s a confusing method of showing the gradients as vectors within a 2D plot.