I was going to ask this as an aside in this question, but I remembered that there are no asides in StackExchange.
Say I've done this again:
I go out and I plant two rows of beets, two rows of turnips, two rows of radishes and two rows of carrots.
Given beets, carrots and radishes like 18 inches between rows and turnips like 24 inches between rows. How close do I plant the first row of turnips to the last row of beets and how close do I plant the last row of turnips to the first row of radishes?