Google implemented a number of changes to its Maps API Standard Plan. Apps created on or after June 22nd will be subject to a host of new rules surrounding access and limits. Active domains utilizing the APIs prior to June 22nd are grandfathered in to differing degrees depending on implementation.
Have you ever noticed how little sense the placement of zip codes make? Sequential zones are an entire city apart. Sometimes there are even zip codes wholly contained within other zip codes. It takes a visual zip code map to make sense of it. Huge.info has just such a map using an interactive Google Map and custom overlay images.