What Makes a City Boundary?

On the City Health Dashboard, city maps are one of the site’s hallmark features. At first glance, some city boundaries might make you think, “this looks odd” – and you are not wrong! City lines are rarely as neat or straightforward as we might expect, and in this blog, we dig into why that is.  

Some cities, like Charleston, SC look like Swiss cheese, with many gaps within the city’s boundaries. Other cities including Covington, KY, have a long winding shape. And some, like Morris Township, NJ even have large holes in the middle of their boundaries. 

The list goes on. Every city has a story to tell, and its boundaries are part of that story. These eye-catching city boundaries invite us to consider why some neighborhoods, essential infrastructure, and geographic features, were included within the city’s boundaries, why others weren’t, and how these decisions impact the people who live there. 

Where does the Dashboard get its city boundaries?

The U.S. Census Bureau is a federal agency that maintains data and statistics representing the U.S. population. Data are reported for a wide variety of geographies – including states, counties, cities, and others. The Census Bureau maintains boundaries for all its geographies, which includes administering an annual survey to local governments to ensure that their boundaries are up-to-date. 

The Dashboard provides data for several types of Census geographies that fall under the umbrella of “cities,” including Census Incorporated Places (CIP), Census Designated Places (CDP), and Minor Civil Divisions (MCD) (you can read more about the Dashboard’s city selection in this technical document). The Dashboard makes some modifications to these city boundaries, including removing large lakes, rivers, and shorelines from the maps to support the site’s user interface, but otherwise presents them as they are provided by the U.S. Census Bureau. 

How are new city boundaries created?

Cities whose boundaries and governments are legally recognized by their state are considered “incorporated” cities. These cities generally have elected governments, collect taxes, and maintain various services, like fire departments, and infrastructure, like roads. Every state has different laws and guidelines for incorporating a new city. Minnesota, for example, requires a petition from property owners and a public hearing, whereas Georgia utilizes a multi-step process that includes a feasibility study, legislative approval, and a referendum vote. 

Take South Fulton, GA – a Dashboard city that was incorporated in 2017. Its incorporation process took over a decade and was motivated by many factors, including a desire for greater self-determination and control over services and taxes. South Fulton’s boundaries were defined based on which parts of the surrounding county hadn’t yet been incorporated into other cities.

How are city boundaries updated?

City boundaries can change over time, most commonly due to adding (i.e. annexing) adjacent land. For example, Sugar Land, TX annexed two communities around 2017 and you can see its westward growth when looking at Dashboard maps from 2016 vs. 2020.   

Page, AZ is another Dashboard city that underwent a major expansion between 2010 and 2020, almost doubling its land mass by adding area to the northwest of the previous city boundaries. This annexation was primarily motivated by a desire to generate additional sales tax revenue from the marinas and parks contained in the expanded area. 

The frequency of boundary changes varies widely across the country. There are some cities that have had stable boundaries for decades, and others that are updated sometimes multiple times a year! This frequency is influenced by state laws that guide how boundary changes occur. 

Now that we’ve explored how city boundaries are made and changed, let’s return to the three examples at the start of the blog. Charleston’s Swiss cheese boundaries are due to “donut holes”, i.e. properties that receive their services from the county but are surrounded by city limits and have chosen not to join the city. Covington’s long winding shape is due to protracted annexation campaigns in the mid- to late-1990s that added new neighborhoods south of the original downtown area. And Morris Township is one of New Jersey’s many “doughnut townships” that fully surround other municipalities. It separated from Morristown in 1865. 

Although we only included a few examples out of the over 1,200 cities on the Dashboard, many of our cities contain interesting stories about how their limits were drawn. Now you know why some of the city boundaries you see on the City Health Dashboard look so unusual.