In 1996, Peter Childers and his wife, Victoria, started to build a new home on the two-acre lot they’d purchased in Orange County, North Carolina, the affluent jurisdiction that includes the University of North Carolina’s flagship Chapel Hill campus.

Or rather, they thought it was Orange County. That’s what it said on the building permit they received, and where they would be paying their property taxes. But driving to their property one day, they noticed a state road sign suggesting that the lot was actually in Alamance County, where property taxes are much lower.

Curiosity piqued, Childers began poking around county courthouses and U.S. Geological Survey (USGS) topographical maps, quickly coming to believe that the road sign was right. Over the next seven years—as the couple finished the house, moved in, and on paper became residents of Orange County—he tried repeatedly to prove to the county’s tax officials that the border was actually 1,200 feet east of his house, putting the Childers solidly in Alamance County.

But nothing changed until 2003, when the Childers, frustrated by years of fruitless attempts, took Orange County to court—and got the county to concede its error, plus $13,000 in back taxes with interest.

“There was no way they could win,” Childers told me. “There was nothing on their side that could prove the line was where they said it was.”

Borders in North Carolina, like in much of the United States, are disappearing. Lines drawn centuries ago weren’t just marked on maps—they were physical demarcations, denoted by ditches, fences, or markings on trees. But ditches can be filled, fences fall apart, and trees are cut down, and over time these visible landmarks have vanished. In their absence, some cities and counties have become unsure about who should be paying their taxes, attending their schools, and using their services.

“If someone is having a heart attack, who are you going to call?” said Brian Carson, a geographic-information-system specialist with the Orange County planning office. “You don’t want there to be any uncertainty.”

But in North Carolina, there’s plenty of uncertainty. To fix it, Gary Thompson, the head of the state’s geodetic-survey office, also acts as its chief boundary hunter. His work is a study in opposites, a combination of centuries-old maps and cutting-edge technology that allows him to replace long-gone markers like “the dead pine tree” with exact spatial coordinates.

“Two hundred years from now,” Thompson said, “they won’t have to worry about finding that tree.”

* * *

In 1950, a state archivist named David Corbitt published Formation of North Carolina Counties: 1663-1943, an exhaustive history of the formation of the state’s 100 counties, stretching back to the first English colonists in the area. According to the records unearthed by Corbitt, Alamance County was to be carved out of the much larger Orange County in 1849, and each county hired a surveyor to mark the agreed-upon boundary. But Orange County’s representative failed to show up, a frequent occurrence in a job characterized by low pay and sometimes-treacherous work (if the snakes and mosquitos didn’t get to surveyors, unhappy landowners sometimes would).

When the two men finally hit the ground in 1851, accompanied by a team of lumberjacks that would clear their path, they used compasses and long chains known as Gunter’s chains to mark a line “beginning at a gum sapling on the Caswell [county] line and running due South to a birch bush on the bank of the Haw river.”

Presumably everyone knew where that sapling and bush were in the day—and even if they didn’t, land was so plentiful that absolute accuracy was not required. But by the late 20th century, the county line’s exact trajectory was subject to interpretation.

“Our county had one definition of where the boundary was, Alamance had another, and the USGS had a third,” said Carson.

Discrepancies like this one hadn’t been a problem when most of the state was still rural, and tax assessors in adjoining jurisdictions could swap parcels to work out differences. But by the late 20th century, increasing development near these grey zones was stirring unease in county courthouses.

In the 1990s, North Carolina began to digitize old paper maps using a geographic information system, or GIS: computer software that links data like roads, property lines, population density, and floodplains to a specific geographic location. State officials soon discovered that no one really knew what the state actually looked like—different counties’ conceptions of their own borders meant the lines sometimes overlapped, sometimes left gaps, and only occasionally matched up.

Enter Thompson. When a border is in question, he and his team begin by cracking open Corbitt’s book, along with any archival records of early deeds and property grants, to see where the boundary was originally supposed to be. They use GIS software to mark the line on a modern-day map, and then head into the field to check their work.

To ensure accuracy in the field, Thompson uses a global-navigation satellite system that captures signals from both the U.S. Global Positioning System (GPS) and the Russian equivalent, called GLONASS. To make up for any errors in those systems caused by atmospheric conditions, North Carolina has a web of 79 antennas around the state that calculates any inaccuracies and transmits a correction in real time to surveying devices in the field. The result is that Thompson can accurately mark geospatial coordinates down to a spot the size of a quarter.

For example, one segment of the state boundary with South Carolina had been marked on pine trees when it was first surveyed in 1772. More than 240 years later, however, the trees had either died or been cut down, taking the state line’s exact location with them.

But Thompson’s team and his counterparts in South Carolina managed to find colonial property maps drawn soon after 1772 that used some of those trees as property corners. They scanned these maps into their GIS software, and then superimposed them on modern land subdivisions. Amazingly, several distinctively shaped colonial land grants were still visible in modern property lines, allowing them to calculate where the trees had stood in 1772.

But not every county boundary in Corbitt’s book can be recovered this way. Some borders in the western part of the state were described as ridge lines whose exact locations have been lost as mountain tops have been lopped off to build homes. For those, Thompson and his team use Light Detection and Ranging, or LIDAR.

Usually carried in aircraft, LIDAR equipment showers the ground with laser beams and times their return, allowing surveyors to develop three-dimensional topographical images and identify physical features like a ridge line, which would take weeks to resurvey on foot, in just a few hours. LIDAR can also help find causeways or roads mentioned in archival records that are now hidden or overgrown. Yet another laser-powered device called an Electronic Distance Meter allows distances of several thousand meters to be measured down to the last millimeter without having to drag a chain through the woods.

Thus far, Thompson has managed to unearth only about a fifth of North Carolina’s original county lines—but the rapid development in ambiguous county-border zones across the state means cases like the Childers’ will become increasingly common. For example, Alamance County’s attempt to clarify its border with another neighbor, Guilford County, foundered last year when Guilford County realized its tax base could lose $8.5 million in newly built homes along the county line.

“We tell the counties, ‘Don’t wait until there’s a problem,’” Thompson said. “Because once there’s a controversy, it makes it harder to settle.”

On the Orange and Alamance county line, however, peace has been restored. Thompson’s team resurveyed the boundary after the Childers’ lawsuit in 2008. When it re-emerged in unexpected locations, the counties allowed homeowners within 150 feet of the line to pick which county they wanted to live in, and moved the boundary accordingly. The North Carolina General Assembly approved the results in 2013. Now instead of a straight(ish) line from the gum sapling to the birch bush, the counties share a jagged saw-tooth-shaped border.

But at least their residents finally know where they live.