From Wikipedia: "a fictitious street included on a map, often outside the area the map covers, for the purpose of "trapping" potential copyright violators of the map, who will be unable to justify the inclusion of the "trap street" on their map."
Thanks, Minerva! I mentioned that fictitious street device on mountweazel but I didn't know an actual phrase existed to describe it. And I'm with you on the getting lost part. :-)
Actually, I lived very near a mountweazel at my last home--online directions always told me to go in the wrong direction to get somewhere, and I finally figured out why after I took a good long look at the maps.
Reminds me of a story I heard in graduate school, of a scholar who invented a reference in his monograph of (say) ants of the world. Twenty years later he published a list of those who'd cited the imaginary work, as evidence of their sloppy scholarship. Perhaps apocryphal, certainly cautionary.