Identifying meridians through examining the location of diseases means to identify the involvement of the meridians in the pathological conditions according to the distribution of the meridians where disease and pain occur. Take headache for example. The yang meridians run up to the head, but distribute differently. Yangming meridian runs up to the forehead, shaoyang merdian to the lateral side of the head, taiyang meridian to the posterior side of the head, and jueyin meridian to the vertex.
Therefore headache over the forehead indicates the involvement of the yangming meridian, migraine indicates the involvement of the shaoyang meridian, and so on. Another example is toothache, the upper toothache is related to the foot-yangming meridian while the lower toothache is related to the hand-yangming meridian.