a digitizer is a computer input device which converts analog information into an electronic equivalent in the computer's memory. in this treatise and its application to computerized cephalometrics, digitization refers to the resolving of headfilm landmarks into two numeric or digital entities – the x and y coordinate. 3d analysis would have third quantity – z coordinate. superimposition cephalometric radiographs can be superimposed on each other to see the amount of growth that has taken place in an individual or to visualize the amount of movement of teeth that has happened in the orthodontic treatment. it is important to superimpose the radiograph on a stable anatomical structures. traditionally, this process has been done by tracing and superimposing on cranial landmarks. one of the most common used methods of superimposing is called the structural method. structural method according to american board of orthodontics, this method is based on series of study performed by arne bjork, birte melsen and donald enlow. this method divides superimposition in three categories: cranial base superimposition, maxillary superimposition and mandibular superimposition. some of the important landmarks in each category is listed below as per the structural method. cranial base superimposition the inner contour of the anterior wall of sella turcica walker point the anterior contour of the middle cranial fossa the contour of the cribriform plate details in the trabecular system in the anterior cranial fossa. the contours of the bilateral fronto-ethmoidal crests. the cerebral surfaces of the orbital roofs mandibular superimposition the anterior contour of the chin the inner cortical structure at the inferior border of the mandibular symphysis. trabecular structures in the mandibular symphysis. trabecular structures related to the mandibular canal. the lower contour of a molar germ maxillary superimposition the anterior contour of the zygomatic process