The language is fairly intuitive, but here is a manual . The following options change the way that DOT does the graph layout and the style. Most of these can be abbreviated to 4 letters. See the DOT manual for more layout and attribute info. These specify that the output should be in portrait or landscape orientation.
Landscape is the default.
These specify the DOT should or should not try to save space by concentrating edges. Default is to concentrate. These specify whether the graph output should fill up the page or not. Default is to not. This specifies some graph attribute to set to some value.