Convoy Trucking

A general question that came to my mind last night, do all server needs solids if they've spawn points on custom mapped island? Judging by the fact that PL have spawn points over custom maps too.

If not, how do they prevent player from falling into water? And why do we need them then?

Im aware about the concept of solids and houses on CT but would like to know how it works on other servers.

spawn 2m above map, freeze player for 0.1*n seconds (n=ping/100), unfreeze player
spawn player 4m above map
teleport player to spawn coords every 50ms for 3 seconds after spawning
ive also seen some servers that have their maps available for downloading from their forum and then they dont use any other special methods to keep from falling

There are no solid objects used in PL for spawn points of players. It uses pretty much the same concept as Fish said. In case if a player falls through the floor because of his lag, the server as no time limit until he can re-attempt to spawn again, which comes as disadvantage to CT who has a 60 seconds wait period which I can never understand why.