20250210 16121300 1.0 TRUE 1990 Block Groups 1990 Block Groups from the Michigan Geographic Framework (MGF) base map. Block groups (BG’s) are combinations of census blocks within a census tract or BNA that share the same first digit in their identifying numbers. For example, BG 3 within a particular census tract comprises all blocks numbered between 301 and 399. A census tract or BNA contains a maximum of nine BGs. BG90 consists of the 6 digit tract number followed by the 1 digit block group number.