From AMS Glossary
Contrary to mathematical convention, individual wind vectors at selected levels are plotted, typically on a polar coordinate diagram, from the region of the diagram toward the direction from which the wind blows. The lengths of the vectors are proportional to the corresponding wind speeds. The sense of each vector is toward the origin. The lines joining the starting points of airflow at successive levels form a hodograph (or hodogram). Each such line corresponds to the wind shear vector in the layer concerned.