We are often asked how often Google updates the imagery in Google Earth. The answer depends on where you live and can be anywhere from once a week to never. For much of the world, there are certain hotspots that get fairly regular updates and other places that have no high resolution imagery whatsoever. To get an idea of where the hotspots are, see our posts on historical imagery density.
The continental US is a special case as it has complete coverage with aerial imagery that is updated over time in large patches that are not concentrated around particular points of interest. The US government has had various aerial imagery gathering programs in the past whose imagery Google has since acquired and put into Google Earth. These appear to have often been done state by state, or at least the imagery Google acquired often follows state boundaries. More recently, however, Google has had its own imagery collection program. So, we decided to see whether or not they are managing to cover the whole of the US and just how long that takes. We used the Google Earth API to map out imagery of the continental US for the last 20 years.
And if you wish to see the data in Google Earth, download this KML file.
Keep in mind that the areas shown are slightly larger than the actual imagery.
We believe Google started gathering imagery around 2012 and the change in patterns is noticeable in the above animation. Instead of following state boundaries, Google appears to gather imagery in what appears to be a random pattern. Analysing the data from 2012 onwards, we believe Google is covering the whole country roughly every three years. There is just one little area in Nevada that seems to have been missed.
We must keep in mind that if you are using Google Maps when there is 3D imagery available, that is what is shown, and that is not included in our analysis here, as the dates and extents of 3D imagery is not available via the Google Earth API.