The remarkable efforts of Citi Bike operators to keep stations stocked around New York City was highlighted last week in the New York Times. Despite their good work, however, many stations still often run out of bikes. My nearest station at 57th and Broadway is typically empty if I don't get there before 8 o'clock, and other stations are worse.

To identify the hardest places to get a bike, we turned to UCL CASA digital cartography researcher Oliver O'Brien, who already runs a real-time map showing how many bikes are at every station.

O'Brien offered the following map of the most frequently empty stations. He notes that emptiness rate may be elevated for new stations that were not immediately stocked after they were installed, such as two high readings in Brooklyn.

"The more significant pattern is the clustering around Central Park — clearly a genuine problem there," O'Brien writes.

TIME SPENT EMPTY: Green = <10%, Yellow dot = 10%-15%, Red dot = 15%-20%, Red pin = 20%+

Empty bike racks are annoying, but full bike racks can be an even bigger problem.

"If the station's empty, you can just go and get the subway or a bus. If it's full, and you are on a bike, you have to cycle around (with the meter running!) to find a nearby one that is not full. That's more of an issue and the reason why the world's more popular systems tend to reduce the bike/dock ratio — somewhat counterintuitive, but sometimes a system works better with fewer bikes in it," O'Brien writes.

Below is a map of the places where it's hardest to park a bike, led by Alphabet City.

TIME SPENT FULL: Green = 0-2%, Yellow = 2-3%, Red = 3-4%, Red pin = 4%+