GE:S uses script files to determine critical gameplay information about a map and how it should be used on rotation. These allow for full customization of your server map and gameplay rotation.
A map script file should go in scripts/maps and use the exact map name as its filename, minus extension (ge_archives.bsp becomes ge_archives.txt). All files there by default can be changed on the whims of the server owner, with default.txt applying to all maps that don't explicitly override its settings, and all maps that do not have a map script file.
BaseWeight : The weight the map has at its ideal playercount
MaxPlayers : Highest playercount on the server before the map will no longer be considered for selection
MinPlayers : Lowest playercount on the server before the map will no longer be considered for selection
ResIntensity : Amount of memory the map uses, used to determine when to take measures to prevent client crashes.
TeamThreshold : Playercount required before teamplay gets enabled on teamplay capable modes.
WeaponsetWeights : Weaponset names contained in the brackets following this keyword will have their random selection weights overridden with whatever is specified. If they are not included at all in a given gameplay's loadout list, the weight will not be overridden.
GamemodeWeights : The random selection weights of the gamemodes you want to be played on your map. If a gamemode is listed in default.txt it will use that weight on all maps that do not specify a new weight. If a gamemode is not specified at all it will not come up in rotation.
TeamGamemodeWeights : Same as gamemode weights, but this selection pool will only be used if the map is switched to when the playercount is above its team threshold.