If this option is set to true TinyMCE will use tiled images instead of individual images for most of the editor controls. This produces faster loading time since only one GIF image needs to be loaded instead of a GIF for each individual button. This option is set to false by default since it doesn't work with some DOCTYPE declarations.
Example of usage of the button_tile_map option:
tinyMCE.init({
...
button_tile_map : true
});