Spatial Anchor Information in the JSON file

I noticed the AchorPosX, AnchorPosY, and AnchorPosZ change every time when I turn the device on. What's this piece of information used for if they change all the time? Also, Can you explain what PPMappings are? For example, what is PPtoAnchorPosX, and how that is different from AchorPosX?

Curious, where did you get the Json file from?

I exported the space from ML2 and downloaded it. It's in the zip folder