As far as I've read and seen for myself, they don't plot over designs! Its super long, but you can place patterns in specific places and cover up all free space to make sure that they only plot in areas you want them to! It's such an amazing new feature for those of us who put so much effort into our town layouts ;;o;;
OMG WHATTTT??? This thread made my day! I didn't even know this was a thing! I'm about to lay so many paths down the next time I am expecting someone to move in. lmao