I didn't make it!
Is it possible to change the map size in single player to 32 or 64 or is this only an option for online.
Not that I know of, though I don't know how to modify. Try this though, it's a good mod: http://battlefield2.filefront.com/file/COOP_Modifier;45461 It enlarges the amount of bots in game, and gives 32 to 64 size maps. Also makes bots tougher to fight. There is a higher version: 4.0 but it had some bugs. I recommend this highly but you might want to get a bot modifier here: http://battlefield2.filefront.com/file/Bot_Changer;48228#Download Use this is the bots seem too smart and if your system is starting to slow down I recommend changing the bot number to 28 which gives you many enemies but not too many. The number of bots that you face should be changed depending on your system hardware. Enjoy:)
My mistake do not use the bot modifier that I posted it seems to not allow the mod in it's list.
To do it yourself without a bot mod, try this:
To increase the number of bots used in singleplayer mode, go to your \Program Files\EA Games\Battlefield 2\mods\bf2\AI directory and open the file aidefault.ai with Notepad or Wordpad. Read the instructions in the file, and remove the words 'rem' from in front of the relevant lines. To alter the number of actual bots, edit the number at the end of the aiSettings.setMaxNBots 32 line (e.g. aiSettings.setMaxNBots 64 for 64 bots). Note that more bots can really stress your system and hence destabilize it.
For mods, tweak the same file in the respective mod folder
You could also download the mod Allied Intent (690 mb), as it has some great SP/coop support. By default it allows up to 64 player map sizes without tweaking it.
What about map size though, Allied Intent doesn't let you do much ground combat it's always air.