Peter Katz (Handout/Handout)

Katz and his boss Robert Brosnan, both blamed the separation on a bad “fit” between Katz’s background in which he primarily worked as a consultant, and the demands of a local government official.

“Despite our mutual efforts over the past few months, it seems we are now unable to achieve the optimal fit to best advance the goals of this position,” Katz said he wrote in his resignation letter.

“As a planning director, you do everything you can to continuously upgrade the quality of projects that are moving through” the department, Katz added. “Arlington has been unusually successful at urbanizing... and its citizens have a very high level of sophistication around these issues.”

Brosnan, director of the Department of Community Planning, Housing and Development, said although the county had carefully vetted Katz before hiring, “you never know until you get someone in if it’s going to be a good fit.”

He said the county will begin a new search for “the critical job” of planning director. The position pays $150,000.

Brosnan was the director of the planning division before ascending to his current job last year. In an interview last December discussing Katz’s first months in the county, Brosnan said coming to an area with “its own way of doing things” would be the trickiest part of Katz’s transition.

“The biggest navigation for Peter is he’s coming in from the outside and doesn’t know how Arlington works,” Brosnan said at the time, adding that Katz was handling the adjustment well.

Katz, 57, started his job in October. The native of Corvallis, Ore., is a proponent of new urbanism, which he described in interviews last year as the way communities are structured.

He was the founding executive director of the Congress for the New Urbanism, a non-profit aimed at making areas walkable and sustainable rather than sprawling. The group held its first congress in Alexandria in 1993.

“I think it’s fair to say that we on the Planning Commission are disappointed because Peter is not only a well known planner, but personally engaging,” Stephen Sockwell, chair of the county’s Planning Commission, said in an e-mail on Wednesday. “He brought a lot of energy to the planning process and we’re sorry to see him go.”

Before coming to the county, Katz had been a planner in Oceanside, Calif., and was in charge of smart growth and urban planning in Sarasota, Fla. He had also been a consultant, which included time advising Arlington County on Columbia Pike development.

Katz’s wife and their two children moved to Northern Virginia a few months after he started the job. He said on Wednesday he thinks they will stay in the area.

During his brief tenure with the county, his seventh-floor office in Courthouse overlooked the bustling Clarendon and Wilson Boulevards. He could see the crowded roadways below, bordered by busy sidewalks and tall buildings, and look beyond that to streets lined with trees and houses stretching into the distance.

He described this in an interview last year as part of the bargain struck in an area that’s part-urbanized, part-suburban: Dense stretches like the Rosslyn-to-Ballston corridor have boundaries between these areas and suburban homes.

When he was hired, Arlington County touted him as the author of the ‘seminal book” on new urbanism. During the five months he worked for the county, Katz started the Rosslyn sector plan and introduced new planning practices to the county as it worked on a major in-fill development for Pentagon City, Brosnan said.

“There wasn’t anything broken that we brought him in to fix,” Brosnan said. “He acknowledged to me that Arlington has some of the best examples of New Urbanism on the ground.”

Arlington is in the midst of trying to manage both residential and commercial growth while also dealing with serious transportation and affordable housing issues. The redevelopment of the Clarendon corridor is considered a model of a vibrant, walkable neighborhood, but not all areas want a Whole Foods and a Crate and Barrel store.

The proposed redevelopment of the working-class neighborhood along Columbia Pike has been particularly thorny. Katz advised both staff and elected officials on that initiative before he was hired, suggesting a strategy for how to regulate development in the area.