@lme56 I updated the methodology doc with a few things after hearing back from the Advan team.
Number of CBGs and Census Tracts in Trade Areas.
Advan cuts the number of CBGs in a trade area to the top 1,000 and number of tracts in a trade area to the top 400 for each POI. SafeGraph did not. This is a temporary measure to limit the size of the data and make it easier to ingest. Advan generates home/work trade areas as 4 fields - geohash 6 (i.e., g6), g5, g4, and g3, so the more distant areas have lower granularity. Advan reserves the right to modify the schema in the future to similarly reduce the overall data size without losing granularity at the local level.Effect: the visitor columns (visitor_home_cbgs, visitor_home_aggregation, etc.) will contain a much smaller number of CBGs / Census Tracts. Additionally, CBGs / Tracts that are distant from the POI (and less likely to have significant visitation to the POI) will be missing. Advan also filters CBGs that did not have enough visitors, so if there are very few visitors and there are 1 or 2 visitors per CBG then these will not show up; in extreme cases that can lead to a blank field.
Panel Details
Note that currently the trade area data use a different panel than the one used for visits, so visits and trade areas do not go hand in hand. Advan is planning on changing that in a future release (no ETA yet). This allows Advan to use a larger panel for the home/work data as a way to analyze a larger and more detailed demographic area. However, because this panel is not sourced as consistently as the panel they use to count visits, it may vary more from month to month.They’ve recently added a new panel provider for the home/work data that is much more stable. The month over month volatility of the trade area panels will be significantly reduced going forward (starting with the November 2023 data).
https://community.deweydata.io/t/safegraph-advan-methodology-differences/26163