They have to plot around gravity masses, stars/planets/blackholes. The Hyperspace lanes are just areas devoid enough for safer travel. Now it says unknown but it’s a misnomer as some of it was once known but years and Sith Wars lead to knowledge being lost and people paying to have systems “lost” from the mapping archives.

You hit a hyperspace lane it’s clear and fast sailing, you go where you have no clue or maps and your odds are crappy. At least if I’m recalling anywhere near correctly.