Some job records do not have a zip code listed on the vacancy and in some cases, a city may have more than one zip code which is where you may see one zipcode with a higher than expected count of jobs. 

An example of higher than expected job counts in a particular zip code is in the city of New York, NY, 10007, which has over 80,000 jobs. Many of these jobs do not list a zip code on the vacancy. 

When no zip code is used, a default value is used.