The original Cargo Deck 'set' had been built with no apparent way for the cargo pods (created by the Production Designer) to get in or out.
When Douglas Trumbull was put in to head up the Special Effects, he asked me to come up with a logical way the Cargo Deck could be accessed - so this was a layout I created to facilitate that. That also gave me the opportunity to visualize the warp & impulse power systems at the same time.