keyboard layot editor

hello i want to edit keyboard layot i.e. make custom(new) keyboard layot is there any keyboard layot editors, or if keyboard layot files can be edited easily with text editor say please, and even that files are not easily editable say please where are ubuntu's keyb. lay. files, and where they are in other type gnu/linux op. systems or maybe it depends on window manager (desktop).
i think it(editor) exist in other case how made(created) that (existing) keyb. layots(?) say please also about where is information about k.l. files format. (and i myself will search more..)