In this paper, we present a method to obtain symmetric and asymmetric reciprocal space maps (RSM) for group-III nitride multilayers on an absolute scale, regardless from the film or substrate lattice constants. The great benefits of full reciprocal space mapping for nitride alloys, in the case of a diffractometer incorporating a position sensitive detector, come at no additional expense in measurement time compared to performing conventional x-ray rocking curve analysis. Additionally, with RSM placed on absolute scale important parameters for device design such as lattice strain and chemical composition, can be unambiguously disentangled and quantified. Some advantages of RSMs in an absolute scale are briefly illustrated with reference to the structural characterisation results from light emitting InxGa1-xN/GaN heterostructures.