Yes it is an XY chart.
I found in the book:"Principles of microeconomics" this txt
// COPY//
The axis contain measurement scales that intersect at 0 (zero).
This point is called the origin.
On the vertical scale, positive numbers lie above the horizontal axis (that
is above the origin) and negative numbers lie below it.
On the horizontal scale, positive numbers lie to the right of the vertical
axis (to the right of the origin) and negative numbers lie to the left of
it.
Each axis is a measuring scale.
.......
So only the upper right iquadrant is positive.
//end of copy//
Zekni
