With more than 500,000 rooms available to rent on any given night, Airbnb now ranks among the largest hospitality companies in the world. But the homes and apartments on Airbnb aren’t owned by employees, so it can be tough for the fast-growing startup to control the experience being delivered to customers. In an effort to help ensure travelers get a stay suited to their tastes, it rolled out the Neighborhood Project, which charts the character of its numerous locations.

And that’s where Zach Walker, Airbnb’s lone cartographer, comes in. In little more than a year on the job, Walker has helped slice and dice more than 70 big cities into 4,500 distinct neighborhoods with their own personalities. "It used to be when you searched for places to stay in New York, the first thing that came up was a bunch of listings in Times Square, the most generic location, " explains Walker. "You could organize by price, but not much more. As we’ve rolled out neighborhoods, people are increasingly booking stays way off the beaten path. It’s opening up the whole city to them."

"People are increasingly booking stays way off the beaten path."

The impact on business, according to Airbnb, has been significant. Neighborhood listings are driving new visitors to the company’s properties through web searches for specific hot spots. And neighborhoods have become the number one criteria renters use when booking, as lesser know areas that once would have seemed unwelcoming or unsafe to travelers are transformed into hip locales in  the process.

"Neighborhoods are the layering of history and culture onto geography," says Timothy Crimmins, director of the Center for Neighborhood and Metropolitan Studies at Georgia State University. This identity can have great value as a brand, something Airbnb has leveraged through Webster's maps. "When you help people to connect with the character of a neighborhood, it can be a real catalyst for business and development, or in this case for tourism."

Walker didn’t know much about map making when he first arrived in Manhattan as a newly minted college grad with degrees in physics and creative writing. But he responded to a Craigslist ad from a startup called Nabewise, a service that created detailed profiles of neighborhoods to help people decide where to move. He fell in love with charting the makeup of big cities. "Each city has its own personality, from the way it’s constructed and organized to the way people and goods flow through."

In July of 2012, Airbnb acquired Nabewise and Walker became their resident map maker. "In a way it’s a tough job because you are trying to define something amorphous," he explains. There is rarely an official boundary for where one neighborhood begins and another ends. "I try to get into the mind of the city as if it were a living, breathing thing," says Walker. He reads up on the area’s history and cross references that with the information from Airbnb’s hosts, crafting data visualizations of keywords from the listings written by users.

"Sometime they have a real argument about the dividing lines, but usually they just want to charge more."

"In an ancient city like London, where the roads turn in on themselves, it can be mind boggling to try and figure out when you’re in Shoreditch and when you’ve crossed over to Brick Lane," says Walker. "But by studying the data from hundreds of users, the descriptions they use of their own homes, I can begin to see where the shifts occur."

When Walker does his job right, a few people usually get angry. He takes neighborhood boundaries that are flexible and porous and replaces them with rigid lines. "People get upset, they write in to complain: ‘Hey my place should be in the East Village,’ when really it's not," says Walker. "Sometimes they have a real argument about the dividing lines, but usually they just want to charge more." But while a few renters are making less these days, overall Airbnb believes mapping the world is providing a big boost to its business.