LESSON 2 Understanding the data
Today you are going to learn what data are available in terms of geography and the subjects covered in the data.
You will also learn what other circumstances the data could possibly be used for
outside of the purposes of redistricting.
Public Law 94-171 (P.L. 94-171)
directs the Census Bureau to provide states the opportunity to identify small geographic areas
for which specific data tabulations are needed and deliver high quality tabulations for those
geographic areas to the states in a timely manner for the purpose of legislative redistricting.
The data in the 2020 Census P.L. 94-171 redistricting data files are derived
from the response data collected from the 2020 Census.
This decennial, the Census Bureau added data for the group quarters population by major group quarters type.
Let’s take a look at the P.L. 94-171 redistricting data file topics you can access.
The redistricting products contain summary statistics on population and housing subjects.
For the tables that start with P, the P stands for population.
And for the table that starts with H, the H stands for housing.
The official titles of the six tables that will be available to you, are as follows:
The P1 table presents the population break down by race. Redistricting data is offered for White,
Black, American Indian and Alaska Native, Asian, Native Hawaiian and Other Pacific Islander, and
Some Other Race.
It is also available for those who select any combination of these six races.
The P2 table presents data for Hispanic or Latino, and Not Hispanic or Latino by Race.
The P3 table presents Race for the Population 18 Years and Over
The P4 table presents Hispanic or Latino, and Not Hispanic or Latino by Race
for the Population 18 Years and Over
The P5. table presents Group Quarters Population by major Group Quarters Type.
Group Quarters type is broken down into institutionalized and non-institutionalized group quarters.
This table includes the total population counts for
institutional group quarters such as correctional facilities for adults,
juvenile facilities,
nursing facilities, and other institutional facilities
as well as noninstitutionalized group quarters such as college/university housing, military
quarters, and other noninstitutional facilities.
The H1 table presents Occupancy Status.
This table includes total housing unit counts, as well as a counts of occupied and vacant housing units.
When talking about redistricting, it is important that these 3 administrative geographies are
understood. Geography is always a central topic when talking about Census Bureau data because
you must define the container for your data.
These geographies are related to redistricting because they form the container of voters for the respective government representatives.
Congressional Districts are the 435 areas from which members are elected to the U.S. House of Representatives.
The number of representatives per state is updated after each Decennial Census.
State Legislative Districts (SLDs) are the areas from which members are elected to the upper
and lower chambers of the state legislatures.
These are updated after each Decennial Census.
The Census Bureau first reported data for SLDs as part of the 2000 Public
Law 94-171 Redistricting Data File.
Voting Districts (VTD’s) refer to the generic name for geographic entities, such as precincts, wards, or election districts,
established by state governments for the purpose of conducting elections.
Redistricting data are available for these common geographies you see
on this hierarchy chart.
The geographies in the center line of this graphic work like nesting dolls. The smallest level of geography is the Block.
Blocks are aggregated to form a block group, block groups form a tract, and so on.
You may have noticed there are numbers to the geographies. Every geography is given a summary
level code. For example, a tract
is given the summary level code 140
in later lessons you will learn how to use these codes to find data.
As stated earlier, the Census Bureau will, furnish the Government and state majority and minority legislative leaders,
redistricting commissions (when applicable), and the non-partisan state liaisons with 2020
Census population counts for the geographic areas needed to perform legislative redistricting.
So, for example state, Congressional districts, state legislative districts, American Indian
areas, counties, cities, towns, census tracts, census block groups, and census blocks.
You don't see city and town in this graphic, but in Census Bureau terminology, that is equivalent to Places,
or County Subdivision in the northeast.
Let's talk a little bit more about boundaries.
You know that this center line of geographies nest within each other.
So, tracts and blocks wouldn't cross county lines, because they nest inside each other.
So, when looking at tract level data within a county the tract data would be whole or complete.
But what about some of the geographies that don't fall within the center line?
A voting district is a geography used for the purposes of elections
and therefore would not cross a county line. You see how voting districts are of the county.
While Congressional and State Legislative Districts can cross certain
geographies, such as a county, they wouldn't cross a State Line.
Data files for smaller geographies
under these state legislative districts or places could contain tract portion or remainder data.
Another way to think of this is if you overlay a voting district map on top of map of tracts,
you can see sometimes tracts might cover multiple voting districts boundaries.
Data users who need to go into a more in-depth analysis of geographic entities or relationships
can find support through our suite of geographic support products.
Here is a comprehensive list of Geographic Support Products. The 2020 Census P.L. 94-171
Redistricting Data are tabulated based on the geographic areas provided in these products.
These products includes TIGER/Line Shapefiles, Reference Maps,
Block Assignment Files, Name Look-up Tables, and 2010 to 2020 Tabulation Block Crosswalk Tables.
Some data users will prefer to look at the maps, others will prefer to work with the text
files (Block Assignment Files and Name Look-up Tables) to understand which blocks nest within other geographies.
Click on the links to learn more about the products and download them.
When you select a topic such as race from the P1 Race data table and a geography such as
a State legislative district, you will discover the population count for each of the race
iterations in the State Legislative districts.
Analyzing these data is how redistricting officials make decisions about how to delineate their districts.
Now know that the purpose of the Redistricting Data Program is to comply with the law
which 1. provides the data state officials need to redraw the
boundaries of the congressional and state legislative districts
and 2.
provide the data needed so states can comply with redistricting rules or laws.
The general guiding principal of redistricting is designed so that each person has an equal
say of 1 person 1 vote.
This course does not cover redistricting laws and standards, but in general,
legislative districts are drawn so that districts are within an acceptable range of the of the
ideal district population.
The ideal district population number is calculated by dividing the state population by the number of districts.
The Voting Rights Act of 1965 is also tied
to redistricting data because section 2 states that a voting practice is unlawful if it results
in discrimination based on race, color, or membership in a language minority group.
Redistricting can vary from state to state, for example some states have different deadlines, some states use commissions, and other do not.
Because the PL files will be the first 2020 census product release that will include demographic and housing characteristics data for detailed geographic areas.
Some may be interested in accessing these data for a variety of purposes.
many may be generally interested in comparing available data between decennial census
or comparing the 2020 decennial census a new data that is collected over the next 10 years.
Analysts may be interested in combining the tabular data from the PL tables with the spatial geography data and voting data from their precincts.
The 2020 Census Population data establishes the benchmark for future population estimates and projections which is calculated annually.
While more dated and tabulations from the 2020 census will be released in the coming months.
The data provided in this initial data release may also be of interest to those who need data on these topics covered
someone like voting researcher or a grant writer, for example.
Here is what you've learned in lesson 2.
You learned about P.L. 94171 files, the purpose for redistricting files and the subjects
you will find in each of the P.L.94171 data files.
Then we introduce beginner census geography concepts.
So, you can understand how geography is the container for the data you're looking at
and essential to how you access and view data.
We then discussed other uses for the redistricting data
and that they could include comparing datasets or be interesting to various researchers.