Many layers are associated with shapefiles that have geography classified by Geographic Summary Levels. This is particularly true about Federal statistical shapefiles. A shapefile will often include data for only one or a few related summary levels.
Geographic summary levels, or just Summary Levels, are 3-digit codes associated with type of political/statistical geographic areas. Most of the summary level codes described in this section are based on Census Bureau summary level codes and used as a standard, where possible, throughout VDA Desktop GIS and Situation & Outlook.
Geographic summary levels (partial list)
010 United States
040 State
050 County
100 Census Block - http://proximityone.com/geo_blocks.htm
140 Census Tract - http://proximityone.com/geo_tracts.htm
150 Block Group - http://proximityone.com/geo_blockgroups.htm
160 City/Place - http://proximityone.com/americas_cities.htm
310 Metros - MSAs/MISAs - Core-Based Statistical Area (CBSA) - http://proximityone.com/metros.htm
400 Urban Area
500 Congressional District - http://proximityone.com/cd.htm
501 Congressional Community - http://proximityone.com/cc.htm
610 State Legislative District - Upper/Senate
620 State Legislative District - Lower/House
795 Public Use Microdata Area (PUMA)
860 ZIP Code Areas