Guides: How US Geography Data Works
Short, accurate explainers that help you read the numbers on our city pages.
How ZIP Codes Work: Structure, History and Limits
Learn what each digit of a ZIP code means, how ZIP+4 works, and why one ZIP code can cover several cities, counties or even states.
US Time Zones Explained: Zones, DST and Exceptions
A clear guide to the time zones used in the United States, how daylight saving time works, and which states and counties are exceptions.
City, Town, Village or CDP? What Counts as a US Place
Understand the difference between incorporated cities, towns, villages, boroughs and census-designated places, and why it matters for data.
How to Calculate the Distance Between Two Cities
See how straight-line distance is calculated with latitude and longitude, how it differs from driving distance, and how to estimate travel time.
Population Density Explained: Urban, Suburban or Rural?
Learn how population density is calculated, how to convert square kilometers to square miles, and how to read density for a US city.
US Counties and FIPS Codes Explained
Understand what a county is, how five-digit FIPS codes are built, and how parishes, boroughs and independent cities fit in.
How to Compare Cities Before Moving: A Practical Checklist
A step-by-step checklist for comparing US cities by size, density, distance, time zone and nearby places before you relocate.
Why City Population Numbers Differ Between Sources
Learn why the population of a US city can differ between the census, estimates and data sets, and how to read the figures on this site.
Why do these guides exist?
Location data is easy to misread. A ZIP code is not a city boundary, a population figure depends on where the boundary is drawn, and a county can contain dozens of differently named places. Each guide explains one of these ideas in plain language and links to the pages on this site where the idea applies. Read them in any order, or start with how ZIP codes work if you are new to the topic. You can also jump straight to the state directory to see the data in action.