Does anyone know the specific meaning of Heluo Book?

According to legend, in ancient Fuxi, the dragon horse appeared from the Yellow River in Mengjin County, northeast of Luoyang, bringing a "river map" to Fuxi. Based on this, Fuxi became a gossip and later became the source of Zhouyi. Another legend is that when Yu was in Dayu, a turtle emerged from Luohe in Silonen County, Luoyang, carrying a "Luoshu" on his back and gave it to Yu. Dayu succeeded in harnessing water on this basis, so he decided that the world was Kyushu. Based on this, nine chapters of Dafa were established to govern society, which was circulated in history books and named Hong Fan. The Book of Changes says, "Rivers paint, Luo writes and sages write", which refers to these two things.