/education-data-source-nhgis

name: education-data-source-nhgis
description: >-
  NHGIS — census geography crosswalks via Portal: links schools (ncessch) and colleges (unitid) to tracts, block groups, CBSAs (1990-2020). Census demographics NOT in Portal — access NHGIS directly. Use for linking education data to census geography.
metadata:
  audience: any-agent
  domain: data-source
  skill-authored: "2026-02-09"
  skill-last-updated: "2026-02-09"

NHGIS Data Source Reference

IPUMS NHGIS — census geography crosswalks and demographic data for education research. Via the Education Data Portal: geographic crosswalk tables linking K-12 schools (ncessch) and colleges (unitid) to census tracts, block groups, CBSAs, and regions (census 1990-2020). Census demographic variables (income, poverty, race, educational attainment) are NOT in the Portal — access directly from NHGIS via free IPUMS registration. Use when linking school or institutional data to census geography for contextual analysis.

Census geography and demographic data source for education research. NHGIS provides the foundation for linking schools to community characteristics via census tracts, block groups, and school district boundaries.

> **CRITICAL: Value Encoding** > > When accessing NHGIS data through the Education Data Portal (not NHGIS directly), categorical variables use **integer encodings**, not string labels. Always verify the exact codes in the mirror codebook. > > | Variable | Integer Code | Meaning | > |----------|--------------|---------| > | `census_region` | `1` | Northeast | > | `census_region` | `2` | Midwest | > | `census_region` | `3` | South | > | `census_region` | `4` | West | > | `cbsa_type` | `1` | Metropolitan | > | `cbsa_type` | `2` | Micropolitan | > | `geocode_accuracy` | `4` | Did not geocode | > > See `./references/variable-catalog.md` for complete encoding tables.

> **CRITICAL: Portal Data Scope** > > The Education Data Portal provides ONLY **geographic crosswalk tables** that link schools and colleges to census geography (tracts, block groups, regions, CBSAs). These contain geographic identifiers and assignment columns — approximately 35-47 columns per file. > > The Portal does **NOT** provide census demographic data (population, income, poverty, race, education attainment, housing, language, etc.). For demographic variables, you must access NHGIS directly via IPUMS (free registration required). See `./references/data-access.md` for direct access methods. > > This skill documents both contexts: Portal crosswalk data (with integer encodings above) and direct NHGIS census variables (in `./references/variable-catalog.md`, clearly marked as requiring direct NHGIS access).

What is NHGIS?

NHGIS (from IPUMS, University of Minnesota) provides free access to census geography and demographic data.

• **Collector**: IPUMS, University of Minnesota
• **Coverage**: US census data from 1790-present (decennial census + ACS)
• **Content**: Summary tables, GIS boundary files, time series tables, geographic crosswalks
• **Frequency**: Decennial census (every 10 years) + ACS (annual, 5-year rolling)
• **Available years**: 1790-2020 (decennial), 2005-2023 (ACS 5-year)
• **Primary identifiers**: GISJOIN (NHGIS internal), GEOID (Census Bureau standard)
• **Education relevance**: Links school locations to community demographics via census tracts, block groups, and school district boundaries
• **Available through Education Data Portal**: Geographic crosswalk tables only (school-to-census and college-to-census links for census 1990, 2000, 2010, 2020). Census demographic data requires direct NHGIS access.

Reference File Structure

| File | Purpose | When to Read | |------|---------|--------------| | `geographic-units.md` | Census geography hierarchy (tracts, blocks, districts) | Understanding census geography | | `school-geography-links.md` | Linking schools to census areas | Connecting school data to demographics | | `time-series.md` | Historical data, harmonization methods | Longitudinal analysis | | `variable-catalog.md` | Key demographic variables, codes, special values | Selecting census variables or interpreting encodings | | `boundary-changes.md` | How boundaries change between censuses | Handling geographic inconsistencies | | `data-access.md` | Direct NHGIS access methods (registration, Data Finder, ipumspy) | Custom census analysis beyond Portal |

Decision Trees

What geographic level should I use?

Research question about...
├─ Individual schools
│   ├─ School's immediate neighborhood → Census tract or block group
│   ├─ School attendance zone → SABINS (limited years) or block-to-school crosswalk
│   └─ School district overall → School district boundaries
├─ School districts
│   ├─ District-level demographics → School district geographic level
│   ├─ Within-district variation → Census tracts within district
│   └─ District poverty estimates → SAIPE (via Education Data Portal)
├─ Regional patterns
│   ├─ County-level → County boundaries
│   ├─ Metro area → CBSA (Core Based Statistical Area)
│   └─ State-level → State boundaries
└─ Historical analysis
    ├─ Consistent boundaries needed → Geographically standardized tables
    └─ Original boundaries OK → Nominally integrated tables

How do I link schools to census data?

Linking schools to census demographics?
├─ Have school coordinates (lat/lon)
│   ├─ Point-in-polygon → Spatial join to tract/block group boundaries
│   └─ Need tract ID only → Geocoding service or FCC API
├─ Have school NCES ID only
│   ├─ Use NCES EDGE files → School District Geographic Relationship Files
│   └─ Use Education Data Portal → NHGIS source provides tract links
├─ Need school attendance zones
│   ├─ 2009-2012 data → SABINS school areas
│   └─ Current data → Contact school district (no national source)
└─ See ./references/school-geography-links.md for details

What time period data do I need?

Time period?
├─ Single recent year
│   ├─ Tract/block group level → AC