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Version: 4.x

Cell mode

The H3 system assigns a unique hierarchical index to each cell. The H3 index of a resolution r cell begins with the appropriate resolution 0 base cell number. This is followed by a sequence of r digits 0-6, where each ith digit di specifies one of the 7 cells centered on the cell indicated by the coarser resolution digits d1 through di-1. A local hexagon coordinate system is assigned to each of the resolution 0 base cells and is used to orient all hierarchical indexing child cells of that base cell. The assignment of digits 0-6 at each resolution uses a Central Place Indexing arrangement (see Sahr, 2014). In the case of the 12 pentagonal cells the indexing hierarchy produced by sub-digit 1 is removed at all resolutions.

Child hexagons are linearly smaller than their parent hexagons.

H3 Cell Index​

An H3 Cell index (mode 1) represents a cell (hexagon or pentagon) in the H3 grid system at a particular resolution. The components of the H3 Cell index are packed into a 64-bit integer in order, highest bit first, as follows:

  • 1 bit reserved and set to 0,
  • 4 bits to indicate the H3 Cell index mode,
  • 3 bits reserved and set to 0,
  • 4 bits to indicate the cell resolution 0-15,
  • 7 bits to indicate the base cell 0-121,
  • 3 bits to indicate each subsequent digit 0-6 from resolution 1 up to the resolution of the cell (45 bits total are reserved for resolutions 1-15)

The three bits for each unused digit are set to 7.

Bit layout of H3Index for cells​

The layout of an H3Index is shown below in table form. The interpretation of the "Mode-Dependent" field differs depending on the mode of the index.

0x0F0x0E0x0D0x0C0x0B0x0A0x090x080x070x060x050x040x030x020x010x00
0x30Reserved (0)Mode (1)Reserved (0)ResolutionBase cell
0x20Base cellDigit 1Digit 2Digit 3Digit 4Digit 5
0x10Digit 5Digit 6Digit 7Digit 8Digit 9Digit 10
0x00Digit 10Digit 11Digit 12Digit 13Digit 14Digit 15