When drivers roll through the south Denver metro area, it can be difficult for them to tell when they’re in Centennial and when they aren’t: Centennial’s boundaries twist and weave throughout much of the city, making for a complex map.

On a trip across Arapahoe Road, residents might ask: Is this part of Greenwood Village? Is it Aurora? Is it Centennial? None of the above?

Residents might be surprised to find that Centennial’s map used to have even more holes in it. The city government has acted to annex more land into its boundaries in numerous years since 2001, when Centennial was legally established as a city.

In 2000, 77% of about 28,000 voters in what is now Centennial chose to create the city, forming a government that was more directly accountable to them. Before then, the residents had to rely on Arapahoe County’s government, since the area was unincorporated.

Large areas of unincorporated land sit next to Centennial’s boundaries. As a city, Centennial has the power to annex that land in some cases, expanding the city’s borders.

When a city annexes land, it must provide services such as law enforcement, road maintenance and other city functions to that area. The land also becomes governed by city ordinances, or city laws.

Depending on the type of land a city annexes, the city may gain some tax revenue — although there can be other benefits to annexation too.

Centennial recently completed an annexation at the intersection of Potomac Street and Broncos Parkway in the central Centennial area, about halfway between Interstate 25 and Parker Road.

Eventually, Centennial could keep expanding its borders if city officials decide to. Here’s a look at what areas are still unincorporated, whether that may change and how annexation works.

Where are the gaps?

Type in “Centennial” on an internet map search, and the label “Dove Valley” might pop up south of Centennial’s central region.

Dove Valley, an area with much vacant land, sits generally south of Arapahoe Road and east of Centennial Airport. Much of Dove Valley is unincorporated.

Along with the unincorporated Inverness Park business corridor — the area that roughly sits between I-25 and Centennial Airport and between Geddes Avenue and the E-470 toll highway — Dove Valley makes up one of the large gaps in Centennial’s map.

Other big holes include unincorporated areas near Smoky Hill Road in the east Centennial area.

See how nearby cities border Centennial — and what areas are unincorporated — on the county's map here.

See a map that shows Centennial’s annexations over time here.

Why do cities annex land?

When a city expands its borders, a few changes happen.

Depending on the type of land the city annexes, the city may receive more sales-tax revenue, as well as a type of revenue called construction-use tax for new development that may happen in that spot, according to a Centennial spokesperson.

But the effects of annexation can also be broader.

“Annexation can provide a variety of benefits to the city including revenues, identity (and) land use control,” said Allison Wittern, Centennial spokesperson.

That’s a reference to how zoning — a city’s rules for what can be built where — comes into play.

Pulling properties into Centennial’s boundaries and the city’s zoning can promote the “character of the area, allowing compatible (land) uses and structures that will create employment opportunities” in Centennial, a previous report by city staff said. In other words, annexation allows a city to have a say in how buildings are developed.

The benefits to the city can also include “boundary consistency,” Wittern said.

“Property owners and businesses often have a clear sense of what jurisdiction they’re located in due to property-specific taxes,” Wittern said. “Short of municipal and county boundaries being painted on the ground, it’s often difficult for the public to know when they are moving between jurisdictions.”

She added: “The city is exploring how to reinforce and establish our unique identity.”

Historically, city officials have been conscious about how people perceive Centennial’s identity, a conversation that has partly touched on efforts such as signage that can make it easier to know when a person is in Centennial.

Why annex residential areas?

Some unincorporated land near Centennial includes residential areas, which, more often than not, “do not generate significant new revenues” for the city when annexed, Wittern said in 2019.

The amount of revenue an annexation could add matters because a city takes on costs when it annexes land — it must provide road maintenance and other city services to that area.

But it’s difficult to determine the exact revenues generated by annexing a residential area, Wittern said in February.

“Undeveloped land has the potential to generate permit and building fees for the city and some taxing authorities. New development also brings new residents and consumer activity to an area,” Wittern said.

She added: “Established residential areas also generate direct and indirect revenues for the city and taxing authorities. With taxation of online purchases becoming nearly ubiquitous, the formula of residential revenue compared to cost to provide services may be changing.”

Annexation without residents’ approval

In many cases, annexing the areas near Centennial into the city boundaries would require property owners to ask for it.

One big exception: the unincorporated Tuscany and Siena neighborhoods near Smoky Hill and Tower roads in the east Centennial area.

Years ago, the city annexed various properties near the Tuscany and Siena neighborhoods, creating an “enclave,” according to Wittern. Enclaves are unincorporated areas surrounded by city land.

Annexing enclaves is a simpler process than annexing other land — it doesn’t require approval by property owners.

Enclaves are eligible for annexation after three years of being an enclave, according to previous city staff reports.

Although the Tuscany and Siena area is an enclave that Centennial could decide to annex, the city hasn’t taken that step.

“The city has not recently engaged the Tuscany and Siena neighborhoods to discuss annexation,” said Neil Marciniak, Centennial’s director of economic development.

Taxes in play

For residents, the possibility of being annexed could raise fears about paying more taxes.

Regarding property taxes, the difference between living in unincorporated Arapahoe County and living in Centennial is negligible, the city has told the Centennial Citizen in the past.

When an area is annexed into Centennial, property owners no longer pay a certain Arapahoe County property tax — known as the Arapahoe County Law Enforcement Authority tax, which supports law enforcement services — and instead pay the city’s property tax.

The county still charges its general property tax on annexed land, but property owners don’t see much change, Wittern has said.

“The net effect to a property owner is negligible,” Wittern said in 2019. For example, the difference between the Arapahoe County law enforcement tax and the city’s property tax was less than an additional $1 per year for a residential property with a valuation of $500,000, Wittern said in 2019.

State law lays out process

Annexing enclaves is a type of annexation provided for by state law, Wittern said, citing state statute 31-12-106. An unincorporated county area must be completely surrounded by a city for a period of at least three years to be eligible for annexation through the enclave annexation process.

Generally, other annexations “require property owner initiation and consent,” Wittern said.

Some of the areas in the city’s map that may seem to be enclaves are partly surrounded by rights of way, or streets, which does not create an enclave, Wittern said.

Where the city could go

In 2019, Centennial enacted what it calls the “Inova III” annexation along Easter Avenue near Peoria Street in the central Centennial area. The city is working on updating the boundary map on its website to include recent annexations, Marciniak said.

When asked whether the city is pursuing or planning for any annexations in the Inverness business corridor; The Farm at Arapahoe County residential area, which sits roughly between Arapahoe and Orchard roads in the east Centennial area; or the land that sits east of Greenwood Village, north of Centennial, south of Belleview Avenue and west of Peoria Street, Marciniak said: “Not at this time.”

Asked whether the city is pursuing or planning for annexation of any of the Dove Valley area or any of the other land that sits between the southern Arapahoe County line and the Centennial city boundaries between I-25 and Parker Road, Marciniak confirmed the city is pursuing some type of annexation in that area.