I am fairly new at officiating basketball so I might not get the terminology correct.

Do you determine a back court violation by where the person's feet, hands, body is in relationship to the back court line or does it only matter where the basket ball is in relationship to the back court?

Neither.

It's a BC violation if the following four elements are met:

1) Team Control
2) The ball reaches the front court
3) A is the last to touch before the ball goes to the back court
4) A is the first to touch after the ball goes to the back court.

If all 4 are met, it's a violation. If even one is not met, it's not a violation.

Read 4-ball location for info on determining FC and BC status of the ball and player.

Additional note....
 

Once front court possession has been established, ANY contact of the division line (including the front edge) by a player in possesion of the ball becomes a BC violation.