The first line of each file is the field header. The types of relationship files and the fields they contain are described below:
| Geographic Area | <entity> | Field Layout | 
|---|---|---|
| Congressional Districts by American Indian Areas | ir | State,AIA,CongressionalDistrict | 
| Congressional Districts by Census Tract | tr | State,Tract,County,CongressionalDistrict | 
| Congressional Districts by County | co | State,County,CongressionalDistrict | 
| Congressional Districts by County Subdivision | mc | State,Cousub,County,CongressionalDistrict | 
| Congressional Districts by Place | pl | State,Place,County,CongressionalDistrict | 
| Congressional Districts by School District | sd | State,SchoolDistrict,CongressionalDistrict | 
| Congressional Districts by Urban and Rural Population and Land Area | ur | State,CongressionalDistrict,TotalPop,UrbanPop,RuralPop,UrbanPopPCT,RuralPopPCT,Arealand, UrbanLand,RuralLand,UrbanLandPCT,RuralLandPCT | 
| Congressional Districts by Zip Code Tabulation Area (ZCTA) | zc | State,ZCTA,CongressionalDistrict | 
Field definitions are as follows: