If anyone cares you can edit the maps now but it's a annoying process requiring the knowledge of hex editor and what not. I'm posting this more so a programmer can kind of figure it out. I don't have the skill to write a GUI (Also the damn SDK is coming out in a month) If someone wants to write a GUI to make this easier then go ahead. But with out a copy of Granny you can't do much.
WARNING WARNING BACKUP ANYFILE YOU CHANGE. IN FACT IF YOU DIDN'T KNOW THAT JUST STOP READING. This is the least user friendly way to do something possible and it's probably better to just say you can't edit the map. This information is more for programmers and people who like code.
This is how to edit Prison
Go to the Demigod/bindata/maps/Map13 Directory (Also known as prison)
Make a copy of the file
MAP13.scmap
This is the contained for the mapping information for prison. You'll need it untouched to play online so be careful and back it up.
Copy the file again and rename the file.
Map13.raw
Open it in photoshop with the following settings
Width 513
Height 513
Channels Count 1
16 Bit
Header 48-Bit
Keep while saving
And you should see a image of prison. This file defines where demigods can walk. Unfortantly it get's more complicated. While it defines where they can walk and the height of the level it doesn't define the edges of the map. Also photoshop seem to enjoy changing the values slightly when you save... YAY for photoshop so writing your own bitmap editor would be easier.
In the MAP13.scmap there is DDS file that contains the edge detail (Side of the map). So work on your file walk data file and then save the raw file.
Open Map13.scmap in a hex editor and use the find utility to find DDS | and | DDS. Copy everything between those two tags and the tags them selves and save them to a file called Map13.dds. Open the DDS file (http://developer.nvidia.com/object/photoshop_dds_plugins.html) and now you'll have the edges of the map. Modify as necsary and save that files as well.
Then in a hex editor replace the Raw section of the file and the DDS portion of the file. And now the demigods can walk in different places in the map but nothing else has changed (YAY)
To change the placement of object spawning points etc you have to modify the LUA files.
To change the models used in the map export them from granny.
Oh and expect the camera to be far to high or far to low for the playing area. That's usually cause the 16-bit value in the walk plane are slightly different then they should be.
