Hierarchical Levels:
Tabulation geographies are organized into nesting parent-child relationships in hierarchical levels. The g0 level is a single unit for the entire country; g1 has the largest units in a given hierarchy, g2 nests within g1, etc. Hierarchical levels commonly, but not necessarily, relate to administrative levels.

Nonstandard hierarchical levels do not fit within the standard hierarchy for a given dataset; for example, sets of selected cities or tabulation geographies representing a previous time period.

Mean Population:
Filtering on mean population is based on the mean population of units within each tabulation geography.

Mean Area:
Filtering on mean area is based on the mean area of units within each tabulation geography.