The Star Tribune requested data on housing code violations at large apartment buildings in Minneapolis while reporting on a lawsuit against Stephen Frenz, owner of The Apartment Shop. That data revealed that The Apartment shop had racked up more violations since 2013 than any other operator of large apartment buildings (4 or more units).

Other landlords with large portfolios, such as Aeon and Sherman Associates, had a very low proportional number of violations. At the other end of the spectrum, it also shows that landlords with just a handful of units often garnered a disproportionately high number of violations.

The city's director of regulatory services, Noah Schuchman, said that may be reflective of the fact that these landlords aren't professional management firms with large staffs. "Your single-building owners, a lot of times, are doing it on their own," Schuchman said, adding that the age of the building can be another major factor.

The Apartment Shop, in late 2012, purchased dozens of rental properties controlled by Spiros Zorbalas, who was forced to sell after the city threatened to pull his licenses. Now, tenants have filed a lawsuit against Frenz, accusing him of fostering similar substandard conditions as the previous owner.

For this analysis, the Star Tribune identified landlords based on the contact names provided on paperwork filed with the city for all rental properties. The contact name is supposed to be the person or management company who is locally managing the property and may not necessarily be the owner. In some cases -- such as the Skelton Family -- the Star Tribune grouped multiple affiliated names. The analysis also required determining the management firms affiliated with different contact names, since the companies themselves were rarely listed.

The Star Tribune only included violations that were issued after the rental license on file with the city was updated to list these individuals or companies as the contact person. An earlier version of this analysis relied on city data which did not make that distinction.

Dan Oberpriller, who scored high on this list, says he is no longer responsible for a number of the properties bearing his name on city records. He is submitting paperwork to have the name changed. Oberpriller leads CPM Properties, a prominent local developer and management firm.

The data does not include single-family and duplex rentals that can be particularly troublesome for city regulators. For example, the data doesn't include all of the properties owned by Mahmood Khan, who is fighting a city attempt to strip his licenses for poor management.

Below is a map highlighting only properties with more than six violations per unit. It shows hot spots in the Phillips, Powderhorn and Near North communities.

The top per-unit violator was 1910 Lowry Ave N., a north Minneapolis six-unit building run by George S. Rea, Jr., with more than 16 violations per unit. The most common orders there were to remove rubbish, repair glass, install or fix smoke detectors, and finish water-damaged surfaces.

Still curious? Use the list below to look up violations at any property with four or more units, dating back to 2013.

Data Drop is a weekly feature that uses data analysis and visualizations to explain, surprise, inform and entertain readers on topics relevant to Minnesotans. Do you have an idea you'd like us to explore? Contact MaryJo Webster