A map point is a relic of the
golden age of raving.
Back in the day, before parties were thrown legally, a good
rave typically involved a renegade group of kids with some generators, sound equipment, and an available empty
warehouse. Most parties were advertised by
word of mouth and minimal flyering, and
permits weren't even a thought.
"Permitz? We don't need no steenkin' permits!"
So what you ended up with was a couple of thousand kids in an abandoned warehouse with lots of flashing lights, loud music, and designer chemicals. As you can imagine, the Powers That Be weren't particularly thrilled with this arrangement, which led to many underground parties being busted.
The solution was to keep the authorities from knowing where the party was for as long as possible. In order to implement this, underground promoters would issue flyers which only included directions to a map point. Once you arrived at the map point, you would speak with a person who would then, at their discretion, either give you directions to the party, or directions to some other place where you'd be left scratching your head, wondering where everyone was.
It is rare indeed to see a party with a map point these days. The closest you'll find is some promoters who don't release the location of venue on their flyers, preferring instead to release the information on an info-line on the night of the event.