Referenced by 5 other explainers
LGA anchoring is how Place Forecast lines up its small-area figures with ABS-published LGA totals for Census-sourced markers.
Each per-group figure at the LGA level matches the ABS figure exactly. We get there in two steps. First, we add up the mesh-block values inside the LGA. Then we scale each group so its sum equals the ABS LGA figure for that group.
The page total may differ from the ABS total by a few people, households, or families. The exact gap depends on the marker. That small gap is perturbation. ABS perturbs each cell on its own. So a published total can differ a little from the sum of its category cells. We anchor on the per-group figures so each group matches ABS. We let the total carry the gap.
Sometimes ABS publishes a non-zero figure for a group, but every small area in the LGA has perturbed to zero. When that happens we spread the LGA value evenly across those small areas. That way the group still appears. A like rule applies inside a small area when its mesh-block values all perturb to zero. The marker page footnotes which groups carry this fallback for the LGA you are viewing.
Per-small-area figures are estimates. They are not separately scaled to ABS. Only the LGA total per group is anchored. Use small-area figures to read shape and trend across an LGA, not as direct ABS counts.