You are here: Census.govGeography › Reference
Skip top of page navigation
Skip top of page navigation


The what, why, and how of Census geography.  What are the definitions of geographic terms, why are geographic areas defined, and how we define geographic areas.  Find reference information such as FIPS and ANSI codes, geographic boundary change notes, significant county boundary changes, and county adjacency information.


Geography Web Atlas

A brief definition of various types of geography along with links to more in-depth information, available data, and maps and mapping tools.

Terms & Concepts

Definitions of geographic terms & concepts used in demographic and housing data products

Hierarchy Diagrams

Graphical representations of how geographic areas relate to each other

Geographic Areas Reference Manual

Detailed explanations of the basic geographic entities from the 1990 Census

Geographic Concepts

Detailed current and historical definitions, delineation information, lists and data files, and links to other products related to selected types of geography

Metropolitan and Micropolitan Statistical Areas

Public Use Microdata Areas

Urban and Rural Classification

ZIP Code Tabulation Areas


Centers of Population

Coordinates for the centers of population from the decennial census, including historical censuses.

Change Notes

Information about selected geographic changes to incorporated places, census designated places, county subdivisions, counties and equivalent areas, and American Indian, Alaska Native, and Native Hawaiian areas

County Adjacency File

List of counties that share borders

Federal Register Notices

List of current and previous Federal Register notices related to census geography

Gazetteer Files

Lists of geographic entities, such as county, place, and census tracts, with information on name, geographic code, population, housing unit counts, and latitude/longitude of the internal point

Geographic Codes

Geographic code look-ups and explanations of the various types of geographic codes and identifiers - ANSI/FIPS, class, functional status, GNIS, LSAD and MTFCC

Guide to State and Local Census Geography

Information about the census geography of each state including a brief history of the state's inclusion in the decennial census

Incorporations, Mergers, Consolidations, and Disincorporations

Lists of incorporations, mergers, consolidations, and disincorporations submitted to the Census Bureau through the Boundary and Annexation Survey (BAS)

Resources for Mapping Census Data

List of interactive mapping applications, other federal government resources, and external national resources.

State Area Measurements

Land, water and total area measurements for the 50 states, the District of Columbia and Puerto Rico as of the 2010 Census

Substantial County Changes

Listing of county boundary changes by decade that affect at least 200 people or involve a large swap of territory



Source: U.S. Census Bureau | Geography | (301) 763-1128 |  Last Revised: July 27, 2015