Though Playerunknown's Battlegrounds now has two maps, it does not have an option to choose which you play. While the devs do plan to add one, for now players have used sneaky tricks to get the map they want. Some disconnect from servers if the randomly-selected map isn't what they want. And, it turns out, some make it simpler by outright removing one map's files. The game does still run, but any time it tries to join a game on the undesired map it'll return right to the menu. One player even made a tool to remove maps easily. It's awkward that there still isn't a map-select option.
Let's be clear: the desert map can do one. While it was an exciting novelty at first and the terrain and buildings can make for interesting firefights, it's far too empty with too many bad looting spots (though the next update will add more buildings and improve loot in some areas, so we'll see) and too few cars and poor pacing across most of a round. So maybe you want to skip Miramar. Or maybe you've played Erangel forever already and want the newness. Whichever.
I'd known of people quitting after joining the lobby and seeing it was a map they didn't want, which is pretty clear from watching the numbers climb down the warm-up then drop by around 20% before everyone gets on the plane. That sucks. It makes for emptier, slower rounds for everyone still playing.
This new trick, which apparently people have been doing since December, is even simpler. Delete or rename the files for the map you don't want and, as I tested, Plunkbat will still run but if you get matchmade onto the map you deleted, it'll kick you right back to the main menu because it can't load the files. It takes about three seconds from clicking play to being back at the main menu. Easy. Even easier if you use this tool to do the renaming.
I suspect that this method still causes the problem of matches starting slim. After being kicked back to the main menu, Plunkbat registered me as being in the match and asked if I wanted to reconnect, so it was still holding a spot for me.
I point this out not to recommend this but because, well, it's happening. The game is missing a feature, and players are taking drastic steps to replicate the effects of that feature - even to the detriment of other players.
I do hope developers PUBG Corp add the map select option soon-ish. I don't know if I'd use it myself--as much as I grumble about Miramar, some of the lads are fans and the variety is welcome--but it would stop the phenomenon of players quitting. I couldn't tell you when I last saw a match start with a full or near-full playercount.