Acquiring and Exploration of Census Data

Last updated on 2026-05-12 | Edit this page

Overview

Questions

  • What kinds of datasets are available from the U.S. Census Bureau?
  • How can you visualize and analyze these datasets for your region of interest?
  • How do you combine spatial and tabular Census data?
  • What variables are available in the ACS dataset?

Objectives

  • Provide an overview of the data available from the U.S. Census Bureau
  • Explain how to download and visualize spatial data from the Census Bureau
  • Demonstrate how to query and analyze the spatial data
  • Demonstrate how to perform complex spatial joins

Introduction to Census Data

The U.S. Census Bureau provides three broad categories of datasets:

  1. Census TIGER/Line Shapefiles
  2. Decennial Census of Population and Housing
  3. American Community Survey (ACS)

Census TIGER/Line Shapefiles

TIGER (Topologically Integrated Geographic Encoding and Referencing) is the Census Bureau’s primary geospatial data product. TIGER/Line shapefiles are available from 2007 to the present; earlier data is available in ASCII format.

These shapefiles include all legal boundaries and names for geographic units across the United States — states, counties, places, ZIP codes, urban areas, census blocks, block groups, and census tracts.

Each record includes a standard GEOID that links directly to Census demographic data.

U.S. Census Bureau TIGER/Line shapefile boundaries for State Regions
U.S. Census Bureau TIGER/Line shapefile boundaries for State Regions

TIGER/Line Shapefiles use American National Standards Institute (ANSI) codes to identify geographic entities, including both FIPS (Federal Information Processing Series) and GNIS (U.S. Geological Survey Geographic Names Information System) codes. For example, the field STATEFP contains the state FIPS code, and STATENS contains the state GNIS code. County-level FIPS codes are five digits: the first two identify the state, and the last three identify the county.

Decennial Census of Population and Housing

Conducted every ten years, the Decennial Census counts every person living in the U.S. at a single point in time, providing the most complete population data with the smallest margin of error.

Variables include:

  • Population: sex, age, race, Hispanic origin, and household composition
  • Housing: occupancy, vacancy status, and tenure — available at all geographic levels, including the highest resolution (census blocks)

American Community Survey (ACS)

The ACS is an annual survey that collects information from a sample of the population. It covers many topics not included in the Decennial Census, such as education, employment, internet access, and transportation. Because it is sample-based, ACS estimates carry a higher margin of error than Decennial Census counts.

The ACS is published in two forms:

  • 1-year estimates — based on 12 months of data; available for areas with populations of 65,000+
  • 5-year estimates — based on 60 months of data; available for all geographies, including small areas

Variables include (in addition to standard demographic and housing data):

Social characteristics:
  • School enrollment and educational attainment
  • Marital status and fertility
  • Grandparents as caregivers
  • Veteran and disability status
  • Language spoken at home
Economic characteristics:
  • SNAP/Food Stamps participation
  • Health insurance coverage
  • Income and benefits
  • Employment location and commute mode
Other:
  • Ancestry, citizenship status, place of birth, and year of entry
Key Points
  • Census data supports planning services for specific population groups
  • It can be used for business and facility site selection
  • It supports public policy analysis
  • It enables spatial analysis of hazard impacts, epidemiological models, and more

Accessing the Census Data

Before mapping or analyzing Census data, you need to obtain it. The Census Bureau provides several access methods:

  • Manual downloads from data.census.gov.
  • Bulk file downloads
  • Programmatic access via the Census API

This lesson focuses on API-based access, which lets you retrieve demographic and socioeconomic data directly into Python workflows — without clicking through a web interface.

What Is a Census API Call?

An API (Application Programming Interface) lets computers request data directly from a server using a structured URL. Census APIs return machine-readable data (JSON or CSV) that can be processed automatically in Python or other tools.

Using the Census API, you can:

  • Specify exactly which variables you want
  • Choose the geographic scale (state, county, tract, block group)
  • Automate downloads for reproducibility
  • Integrate data directly into scripts and analyses

This approach is especially useful for research, teaching, and large-scale analysis.

Typical Census API Workflow

  1. Construct a request URL specifying variables and geography
  2. Send the request to the Census API endpoint
  3. Receive structured data (JSON or CSV)
  4. Convert results into a DataFrame
  5. Optionally join data with geographic boundary files for spatial analysis
Callout

Note on Privacy

Census APIs return aggregate data only. Individual-level records are never provided, ensuring respondent privacy.

Discussion

Getting Started with the Census Notebook

Work through the interactive Python notebook linked below, which covers everything on this page hands-on inside Google Colab. More Reading on Census API below!

This part of the session covers:

  • Part 1: Retrieving the Dataset - You can refer to the theory just below.

  • Part 2: Exploring the Dataset - Structures, variables, columns, geographical units.

Open the Notebook in Google Colab.

Note: After Completion, DO NOT close the notebook. Keep it open as we will use it for the next part of the workshop.

Tutorial: Accessing ACS Data via the Census API

Step 1 — Explore the Census API

  1. Go to the Census Developers Page.
  2. Click Available APIs (left of the search bar).
  3. Scroll down and select American Community Survey (ACS).
  4. The ACS offers 1-year and 5-year estimates. We will use the 2023 ACS 5-Year, which covers data from 2019–2023.
  5. Scroll to Data Profiles and review the “Example Call” links — these are the base API URLs you’ll use in Python or a browser.
  6. Under Data Profiles, click the html link next to 2023 ACS Comparison Profiles Variables to browse all available variable codes.

The ACS API uses different URL patterns depending on the geographic level you want:

  • Country
  • State
  • Tract (within a state and county) For tract-level data, use the state > county > tract pattern. Here is an example for Indiana (state code 18):
https://api.census.gov/data/2023/acs/acs5/profile?get=NAME&for=tract:*&in=state:18&in=county:*&key=YOUR_KEY_GOES_HERE
Key Points
  • tract:* returns all tracts in the specified state
  • county:* returns all counties in the specified state
  • Replace state:18 with your state’s FIPS code (State Codes List)
  • state:* is not allowed for tract-level queries due to dataset size limits — you must specify a state

Step 3 — Add Variables to Your Request

  1. On the variables page from Step 1, press Ctrl+F and search for your variable of interest.
    Example: searching “no vehicles available” returns variable DP04_0058E (the estimate version).

  2. Add the variable after NAME, separated by a comma: Before:

    https://api.census.gov/data/2023/acs/acs5/profile?get=NAME&for=tract:*&in=state:18&in=county:*

    After:

    https://api.census.gov/data/2023/acs/acs5/profile?get=NAME,DP04_0058E&for=tract:*&in=state:18&in=county:*

  3. Add additional variables by separating them with commas:

    get=NAME,DP04_0058E,DP02_0001E,DP03_0062E

  4. Make sure to add the GEO_ID column as well.

Step 4 — Optional Enhancements

  • View variable descriptions: Add &descriptive=true to your URL
  • Download as CSV: Add &outputFormat=csv for a spreadsheet -friendly file
Callout

Heads up: API variable names are case-sensitive — they must match exactly as listed in the variables page.

📺 Video Tutorial: How to Access ACS Data from the Census API

Example: Final API Call

Note: Make sure to add the API key within the link.

https://api.census.gov/data/2023/acs/acs5/profile?get=NAME,GEO_ID,DP04_0058E&for=tract:*&in=state:18&in=county:*&descriptive=true&outputFormat=csv&key=""
This returns the number of occupied households without a vehicle for every census tract in Indiana.
Key Points
  • The Census API gives you flexible, precise access to ACS data
  • You can combine multiple variables in a single API call
  • &descriptive=true adds plain-language descriptions for each variable
  • &outputFormat=csv makes the data easy to open in Excel or import into Python