A flow map is a combination of a flow chart and maps. They are used to see the object moving over a map. In this visualization, we see a map on which flows of different objects are going from one area to the other using arrows with different widths. The width of the arrow is proportional to the quantity of movement.
Why do you need it?
We need flow maps to see the variation of the distribution of an object from an area to other areas. The lengthy data we have is then studied effectively, and the weak portions can be analyzed, and we can adopt respective measures on time.
What kind of data you can visualize with it?
If you have a geographical movement-related data, then flow charts will be beneficial. Assume you have a yearly dataset of distribution of a specific species of birds that migrate every season in Australia. Now we can analyze by the biggest arrow that in which area the birds used to migrate in which season, giving us a sight of their habitat.