The word "somatotopic" is everything relating to the relation between body regions and areas of the brain.
Somatotopic is an adjective derived from the word "somatotopy", which is a noun that refers to the correspondence between an region of the body and an area of the cerebral cortex. "Somatotopic" is a medical term and it is generally used when it is followed by the word "arrangement" in order to refer to this correspondence and; therefore, to refer to brain development.