All radiograph of skull are undertaken with reference to a series of palpable landmarks and recognized lines or planes of the skull.

Landmarks:

• Outer canthus of eye: The point where upper and lower eyelids meet laterally.
• Infra orbital margin/point: The inferior rim of the orbit, with the point being located at its lowest point.
• Nasion: The articulation between nasal and frontal bones.
• Glabella: A bony prominence found on the frontal bone immediately superior to the nasion.
• Vertex: The highest point if the skull in the median sagittal plane.
• External occipital protuberance (Inion): A bony prominence found on the occipital bone usually, coincident with the median sagittal plane.
• External auditory meatus: The opening within the ear that leads into the external auditory canal.

Lines:

• Inter-orbital (inter-pupillary) line: Join the center of the two orbits or the center of two pupils when the eyes are looking straight forward.
• Infra-orbital line: Joints the two infra-orbital points.
• Anthropological baseline: Passes from the infra-orbital point to the upper border of the external auditory meatus (also known as frankfurter line).
• Orbito-meatal baseline/radiographic baseline: Extends from the outer canthus of the eye to the center of external auditory meatus. This line is aligned approx. 10° to the anthropological baseline.

Plane:

• Median sagittal plane: Divides the skull into right and left halves. The landmarks on this plane are nasion anteriorly and the occipital protuberance (inion) posteriorly.
• Coronal planes: there are at right angles to the median sagittal plane and divides the head into anterior and posterior parts.
• Anthropological plane: A horizontal plane containing the two anthropological baseline and infra-orbital line. It is an example of an axial plane. Axial planes are parallel with this plane.
• Auricular plane: Perpendicular to the anthropological plane. Passes through the center of the two external auditory meatuses. It is an example of a coronal plane.