In presenting migration survey results, a map that uses arrows to show the origins and directions of people moving into a town is called a:

A flow map uses arrows, often varying in width, to show the origin and direction of movement, which is exactly what is needed to display where migrants have come from and the routes of their movement into a town. Choropleth maps, dot maps and isoline maps display density, distribution and continuous surfaces respectively, not directional movement between places.