6 / 6 Data & Analytics Pipelines

Rolling Up Hexagons

H3 tiles the globe with hexagons on an icosahedron, with twelve pentagons at the icosahedron vertices. Each finer resolution has cells about a seventh the area of the coarser one, and a child index can be truncated to obtain its parent index.

Resolution Average cell area (km²)
7 5.161
8 0.7373
9 0.1053

A pricing pipeline counts trips per resolution 9 cell every minute. A dashboard wants the same counts at resolution 8 and gets them by truncating each resolution 9 index to its parent and summing. Which statement about that rollup is true?

A

Because a child is a seventh of the parent's area, a resolution 9 count can be scaled by seven to estimate the resolution 8 count.

B

Every resolution 9 index has exactly one resolution 8 parent, so summing children is exact per parent index. But the parent's boundary is not the union of its children's, so that total is not a count of trips inside the resolution 8 polygon.

C

Truncation can map one child to two parents near cell edges, so the rollup may count some trips twice.

D

Each resolution 8 cell has exactly seven children, so multiplying the average child count by seven gives the parent total.