Statewide Database | Redistricting

Election & Census Data
Geography & Conversion

Redistricting Data

The primary conceptual difficulty in creation of this database occurs because of the fact that much of the data that goes into this database is provided in aggregate form, and the data is from different and uncoordinated sources.

Census data: This dataset is produced from the Decennial Census. The P.L. 94-171 file is released on the census block and contains 4 tables reporting Total Population, Voting Age population, race, ethnicity, housing and (new for 2021) and additional table with specific group quarter counts.

Voter Registration data: The Statewide Database collects the Statement of Registration to produce various statistics including partisan affiliation and participation history. These data are surname matched to allow for voting rights analyses.

Election results: Organized by SOV (Statement of Vote) precincts, this data is collected from each of the 58 county elections offices and is used to analyze racially polarized voting under the VRA.

For redistricting purposes, the voter registration and election data are allocated to census blocks.

Conversion and Assignment File Collection

Conversion and assignment files are used for translating data from one geographic unit of analysis to another.

Assignment files are used to assign smaller geographic units to larger geographic units that fully contain them. For example, census blocks can be assigned directly to census tracts because census tracts never split census blocks, and therefore every census block is fully contained within a census tract. Assignment files generally have two columns, one column indicating the geographic unit to be assigned and the second column containing its corresponding assignment to the other geographic unit.

An example of one of our most commonly used assignment files is our block to district assignment file. This file contains the census block numbers and their corresponding assignment to a given set of districts such as Assembly, Congressional, Senate, or the Board of Equalization districts. This is possible because census blocks do not cross district lines and as such they are either wholly within a given district or they are not.

Conversion files become necessary when there is overlap between geographies. As a result a geographic unit can not be wholly assigned to another, as it is only partially contained within another geographic unit. In this case, it's neccesary to 'translate' the geography from one geographic unit to another. Therefore, conversion files will have a third column indicating the ratio of the geographic unit contained with in the other.

For instance, census tracts will often only be partially contained within a given census place. In this case, a census place to census tract conversion file can tell you what percentage of a census tract is contained with a given census place. These percentages can be determined using either the census block population of the tract contained with the census place or the percentage of area of the tract contained with in the census place.

Legislative District Conversions & Assignments: These files can be used to determine the Assembly, Congressional, Senate, and Board of Equalization district of other geographic entities such as census blocks, census tracts, election precincts or zip codes.

Precinct Conversion Files From 2002 Onward: Precinct boundaries change with every election. The precinct conversion files available on the Precinct Geography and Conversion pages are used for merging precinct data to other geographic areas such as census blocks and cities.