Each redistricting dataset merges the electoral data the SWDB collected and processed over the preceding decade with the most current census data (PL94-171). The result is a census block level dataset that allows for longitudinal analysis of electoral data over time on the same unit of analysis. Electoral data consist of the Statements of Vote (SOV) and Statements of Registration (SOR) for each statewide election. These data are collected from the Registrars of Voters for each of the 58 California counties with each election.
The SWDB collects the Statement of Vote and the Statement of Registration along with various geography files from each of the 58 counties for every statewide election. The Statement of Vote is a precinct level dataset and precincts in California change frequently between elections. The goal of the SWDB is to make election data available that can be compared over time, on the same unit of analysis – a precinct, a census block or a census tract.
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: The dataset for redistricting (PL94-171) is based on the level of the census block and has data on population, ethnicity, age, and housing.
Voter data: The Statewide Database collects statistics by using voter partisan affiliation, date of birth, surname, address, and voter history. These statistics are collected from the statewide registered voter file and are reported at the census block level.
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 registration and electoral data needs to be placed into census blocks.
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.
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