Organ fibers and skin fibers from the same spinal level hand their signal to the same cell. The brain knows that level well from the skin and hardly at all from the organ, so it points at the skin. Pick an organ and watch which surface lights up.
Where it is felt brighter means more shared levels
Front view on the left, back view on the right. R and L mark the body’s own right and left, which swap over between the two views. Every patch is a skin field with its own spinal levels. Tap a patch to run the map backward and see which organs could send pain there.
The shared spinal levels C1 down to S5
The top row is where the organ sends its fibers. The bottom row is where the lit skin field sends its fibers. A level in both rows is a place they converge.