Putting a neighborhood on a map is harder than it sounds. If you live in a neighborhood with a name, you probably think you know its boundaries. But do your neighbors agree? Does the local government? Probably not.

While neighborhoods have roots in concrete things like topography, physical barriers, and architecture, they’re also reflections of the people and communities that reside in them. That leaves their precise location open to interpretation.

Boundaries can also be shifted by a huge array of factors, including demographic changes, road construction (or destruction), and commercial rezoning, to name just a few. Realtors often complicate things by stretching the boundaries of desirable neighborhoods to include nearby homes for sale, or simply inventing new names for areas they think are ripe for gentrification. Some of these names end up being adopted by the gentrifiers and eventually find their way onto maps. Other times, the locals rebel.

The size of the resulting neighborhood discrepancies—and the degree to which people care about them—varies among cities. In a place like Boston, both of these factors tend toward the more extreme end of the spectrum. The city’s previous mayor described the neighborhood boundaries as a “hogmosh of undefined lines,” a situation made more volatile by Bostonians’ attitudes toward their home turf.

“I think there is a lot of neighborhood pride in Boston, which can mean strong opinions about territory,” says cartographer Andy Woodruff of Axis Maps. “Everyone in this town seems to be out to prove they're more legitimately ‘local’ than anyone else, so when it comes to neighborhoods there's a lot of, ‘My family has lived in Dorchester for seven generations, so don't try to tell me where the boundary is.’”

Woodruff, along with cartographer (and native Bostonian) Tim Wallace of The New York Times, decided to map those strong opinions by asking Bostonians to put the neighborhoods in their minds onto a digital map. The result is the map at the top of this post, which shows the consensus. The darkest blue areas indicate where 100 percent of the mappers agree, with areas of lower agreement in lighter shades.

The map is based on 2,400 individual neighborhood outlines submitted by hundreds of people over the last five years. The map below shows every boundary line drawn around a neighborhood.

View Images This neighborhood consensus map comprises outlines of neighborhoods submitted by hundreds of people. Map by Andy Woodruff and Tim Wallace, Bostonography

The first version of the neighborhood map, published in 2013 on Woodruff and Wallace’s website, Bostonography, was based on 21 of the neighborhoods on the official Boston city map. The updated version allowed people to add any named neighborhood they believe exists, and extended the map beyond city limits to include areas that are part of the greater Boston metropolitan area. At least five people needed to map a given neighborhood before it was included. (This also helped weed out the jokesters who inevitably invented ’hoods with funny names or obscene shapes.)

Giving people the freedom to designate any neighborhood they wanted yielded some surprises. The map includes neighborhoods Woodruff had never heard of, such as tiny Duck Village, which sits in a little splotch of space near the border between the neighboring cities of Cambridge and Somerville.

And people preferred to break up some larger neighborhoods, such as Boston’s “Downtown,” which was subdivided into Government Center, Downtown Crossing, and Financial District on the new map.

Overall, however, Bostonians didn’t stray all that far from the official neighborhoods on the city’s map. On the map below, which shows the official neighborhood boundaries, you can find a few exceptions, such as Hyde Park (the southernmost neighborhood outline) eating all the way into the 100 percent consensus zone of Mattapan (the neighborhood just to its right).

View Images Official neighborhood boundaries are overlain on the unofficial consensus map. Map by Andy Woodruff and Tim Wallace, Bostonography

Cambridge, on the other hand, looks almost as if people were intentionally avoiding the official neighborhoods. Woodruff says this is because people tend to think of Cambridge as made up of its named squares (most of which are just glorified intersections), from Harvard Square to Kendall Square near MIT. The city map is also arranged around the squares, but with the neighborhoods in between them.

Central Square is a recognizable area of Cambridge, but it doesn’t exist at all on the official map. And some official neighborhoods don’t show up on the crowdsourced map at all, including Wellington-Harrington, where I recently spent a year. It’s just a blank spot between East Cambridge and Inman Square. Even Woodruff’s Riverside neighborhood is missing.

“Mine doesn't even show up on my map!” he says. “Almost all of it is drowned out by Harvard Square or Cambridgeport on the crowdsourced map.”

Of course, this could change in the future. People’s conceptions of neighborhood boundaries shift with time, reflecting the inevitable physical and demographic changes cities constantly undergo. The crowdsourced “official unofficial” Boston neighborhood map offers a way to visualize these sorts of changes as they happen.