Some embodiments of the invention provide a method of routing nets in a multi-layer integrated-circuit ("IC") layout. For each particular net in a set of nets, the method specifies different spacing constraints for routing the particular net in different directions on the same layer. It then defines a particular route for each particular net in the set of nets, where the spacing between at least one particular route and an item adjacent to the route in the layout is different in the different directions on the same layer.