You can enable map voting by putting the mapvote 1 command to the sapp init file (which is found in the sapp folder, which is found in the gametypes folder).
Example: C:\Users\<username>\Documents\My Games\Halo CE\sapp\mapvotes.txt
Write mapvote options to the mapvotes.txt file (put it in gametypes sapp folder as well) like this:
map:gametype:description:min players:max players
bloodgulch:Slayer:Bloodgulch - Slayer:0:16
hangemhigh:Clasic Slayer:Hang 'em High - Classic Slayer:8:12
dangercanyon:CTF:Danger Canyon - CTF:8:16
(Make sure that you have the map and the gametype, and wrote them correctly)
You can specify the amount of displayed mapvotes / round with the max_votes [number] command. The default value is 5.
|mapvotes||Lists every mapvote option.|
|mapvote_add <Map> <Mode> <Description> [MinPlayers] [MaxPlayers]||Adds a new element to the mapvote list. A mapvote option is displayed if the player number is between MinPlayers and MaxPlayers, their default value is 0 and 16.|
|mapvote_del <ID>||Deletes the mapvote with the given 'ID'. (You can get the ID with the mapvotes command)|