Some neighborhood names appear to be jokes. Some have stuck around for centuries, despite changing connotations. Some shift with the winds of gentrification. Welcome to Blurred Lines, in which writer Keith Williams of The Weekly Nabe studies New York City's changing neighborhood boundaries.

The Upper East Side is now one of the most exclusive neighborhoods in the city, but until the mid-1800s, much of the space was open to all. Sandwiched between Harlem Village to the north and the city to the south, most of what's now the Upper East Side was considered Common Landsproperty without an owner. At the beginning of the 19th century, the city began to parcel the land [PDF] for purchase and for rent, but these transactions were speculative, hopeful even, given that the lots were considered to be in the middle of nowhere.

When the area's name was codified in 1896, "The Upper East Side Association of New-York City" took under its wings everything north and east of 40th Street and Fifth Avenue in Manhattan. Fortieth Street was the southern border of the 19th Ward, an old city administrative subdivision, but the opening of the Queensboro Bridge in 1909 created a more natural boundary in 59th Street. Upper East Siders tend to be territorial, so it's no surprise that three historic areas that defined the neighborhood have lingered on: Lenox Hill, Yorkville, and Carnegie Hill.

Even though the area was thought of as a no man's land until the early 20th century (see the above comic), what we now know as the Upper East Side started to take shape well before that. St. James Church was built in 1810, at what is now 69th Street and Lexington Avenue, on Common Lands appropriated for that purpose. It was the only Episcopal church between the Bowery and Westchester. It also sat on a hill, and locals loved flocking to the heights in the summer to escape mosquitos bearing yellow fever.

The hilland the neighborhood that followedwas named after Robert Lenox, a Scottish merchant who purchased land for a farm in 1818. He bought his first plot from the foreclosed estate of Archibald Gracie, a man who had made his home in the area two decades earlier. His home was Gracie Mansion, now the residence of our city's mayor. It was built along the poorly-kept route connecting Hellgate Ferry at 86th Street with the old Boston Post Road in 1799.

By the mid-1820s, speculators had snatched up most of the land around the Ferry Road, and the area came to be known as Yorkville, perhaps after nearby "York Hill," also known as Harlem Heights.

In 1837, the New York and Harlem Railroad opened a tunnel between 92nd and 96th Streets to connect the village of Harlem with City Hall. Now used by Metro North, it's the oldest operating tunnel of any kind in the city. This train connected this new hamlet, centered around 86th Street, with the rest of civilization, both north and south.

Many of the settlers of Yorkville were Germans. What's now called Lenox Hill Hospital, at 77th and Park Avenue, was opened in 1868 as the German Dispensary to serve this immigrant population. Randel's 1811 grid plan included "Observatory Place", a ten-block-square public plaza between Fourth and Fifth Avenues and 89th and 94th Streets. It was closed in 1865, did not house an observatory, and is of no relationship to the "green" building a few blocks north in Harlem.

The Upper East Side was finally filled out toward the end of the 19th century. The Second Avenue and Third Avenue Els opened in 1875 and 1878, and provided added convenience to the area. The German population of Yorkville burgeoned after the 1904 General Slocum riverboat disaster, when over 1,000 immigrants perished after the ship caught fire in the East River near the Hell Gate. (Many emigrated from the Lower East Side to escape the pall of the tragedy.) Later that year, the Times dubbed Yorkville and Italian Harlem to the north as "The New East Side." Today, there are few reminders of this heritage, with the Schaller & Weber butcher shop and the struggling Heidelberg Restaurant notable and well-loved exceptions.

But over the years, the shadowy nature of the Third Avenue El made this area a dangerous, lifeless place, creating an arbitrary dividing line between residential and commercial. Yorkville, and the people who lived there, shifted east as a result, and the area to the west became mostly factories. One exception was the prime real estate on Fifth Avenue facing Central Park. Carnegie Hill is named for Andrew Carnegie's mansion, now the Cooper-Hewitt Museum, finished in 1903. L.B. Elliman, patriarch of a real-estate empire and just 22 at the time, had brokered the sale of land to Carnegie five years earlier.

Geography, too, had made the vicinity an unpopular spot. It was, according to the historic designation report [PDF], "too hilly for farmland, too far inland for river traffic, and too far from lower Manhattan for building speculation." Within a decade of Carnegie's mansion, many of the lots below 96th Street west of the El had been filled with manufacturing buildings.

Although 96th Street has long been the Upper East Side's northern frontier, 2010 census data show that it might be subject to review. Southeastern Harlem saw a 40 percent increase in white residents over the preceding ten-year period, while minority numbers increased below the line. The difference between these neighborhoods is a matter of connotation and culture, rather than one of geography. In the past few years, several realtors, seeking a price bump from the tonier name, have tried to push the boundary toward the triple digits, particularly along Central Park; those efforts haven't stuck. Although the lines might be blurring, they appear to be etched in stone.

· Blurred Lines archives [Curbed]