Hi Paolo,
the concept of positions is really just a way of describing the fact that you can play in different keys on one harmonica. In the key to which the harmonica is tuned (the key designated on the harp), all of the natural (unbent) notes belong to the major scale in that key and there is a complete major scale in holes 4-7. You can see this on the diagram of the tonal layout on a C harp shown above. Using this major scale as the basis for melodies is often referred to as playing in 1st position.
This is great for folk songs and playing in the style of Neil Young or Bruce Springsteen, for example, but it doesn’t sound right for blues harmonica, as the blues often uses notes which do not belong to the major scale. This is why harp players mainly play blues in 2nd position, playing a C harp in the key of G for example. Here the starting point of the scale is not 4-blow, but 2-draw, which is the root note of the draw chord. Because the harp is a diatonic instrument, choosing a different starting point will automatically give a scale with a different interval pattern, so that it also sounds different. The scale produced by the unbent notes becomes progressively less major sounding and more minor sounding as you move from 1st through 2nd to 3rd to 4th to 5th, and the location of the starting point or root note in each position is of necessity in a different hole. Once again, the tonal layout diagram above may help you visualize this.
So you’re right, the system we call positions does relate to a physical coordinate, namely the location of the root note of the scale being used. It’s not a perfect system, but it helps describe what people actually do.