How many years has the Riverside Scene at Qingming Festival been painted?

The Riverside Scene at Qingming Festival is 24.8 cm wide and 528.7 cm long. The scene is grand, grain ships gather and the population is dense. How can such a long historical picture accurately count the number of people?

A calligrapher named Tang made accurate statistics in a simple and ingenious way. He put a grain of rice on everyone in the picture first, and then counted how many grains of rice were put in a * * *. The result is that there are 8 15 people in the Qingming Riverside Map.