Districts are constructed using census geography.
Census geography corresponds with decennial census population counts, upon which district plans must be based.
Except for the last item in the layer list, the 'Standard Reference Overlay', reference layers derive from decennial census geography, and will therefore align with district boundaries.
Non-Census Base Maps
The map makes use of non-census base maps, the features of which may not align precisely with district boundaries.
To resolve specific boundary questions, it is sometimes necessary to refer to the census base geography with which the districts were originally drawn.
The address search function uses a commercial geocoding service.
While locations returned are typically accurate, they should not be considered definitive, especially in rural areas.
Included in the map is a 'Voting District', or 'VTD' layer.
VTDs represent voter precincts as they were captured for the last decennial census.
Though change in voter precincts is typically incremental, precinct geograpahy does evolve over time, leading to some differences between VTDs and current precincts.
ZIP Code Areas
Included in the map is a 'ZIP Code Areas' layer.
The US Census Bureau publishes ZIP Code Tabulation Areas, or ZCTAs, with their decennial census geography release.
For each census tabulation block, they determine the most frequently occuring ZIP code of contained addresses.
Blocks with the same predominant ZIP code are then aggregated to create ZCTAs.