Fig. 4

Hilbert curve and number. a Four basic subdivision modes of Hilbert curve. b The first level of Hilbert curve. c The second level of Hilbert curve. d The third level of Hilbert curve. e Number for each grid cell. a Each subdivision mode includes two basic parts: cups and joins. A cup is a square with one open side, and a join is a vector that joins two cups. b Each grid is represented by a red dot, and the dots are connected by lines to form a cup with bottom opening, which is the first layer of the Hilbert curve. c According to the Eq. (6), the partitions exceeding the density threshold are divided twice. The final Hilbert curve result and a road network data broadcast cycle are shown in d. According to the direction of Hilbert curve and division level, we numbered each grid cell. If a subscript value consists of three bits, that means the cell is acquired by being divided by three times, as shown in e