Ever since we did the posts on historical imagery density we have been looking for a way to map parts of the earth that do not yet have historical imagery. Sadly, the Google Earth plugin does not report historical imagery accurately for such areas.
We recently discovered that the Google Maps API provides a service known as the Maximum Zoom Imagery Service, which allows you to find out what the maximum zoom available in Google Maps is for a given latitude and longitude. The maximum zoom available when in ‘Earth’ mode is dependent on what imagery is available in Google Maps. Since the imagery in Google Maps is almost the same as the default layer in Google Earth, this service can tell us a lot about the imagery in Google Earth.
Today we are just looking at how we gathered the data and prepared it for viewing in Google Earth. In later posts we will look at what is actually in the data and what we can learn about Google Maps and Google Earth imagery.
We queried the Maximum Zoom Imagery Service for every 0.1° from -80° to +80° latitude and every 0.1° of longitude. The result is 5.76 million points of data, which results in multiple KMLs totalling over 1Gb. To display it as a heat map we could have created a KML file with each rectangle as a polygon, but that would probably have crashed Google Earth. So instead we used the technique we used when finding imagery updates and converted the data to an image and displayed that using an image overlay.
If you display each data point as a single pixel, then Google Earth tends to blur the image, so we resized the image to have each data point 4 X 4 pixels. The Maximum Zoom available in Google Maps for the locations we collected varies from 7 to 22, 7 being the lowest resolution imagery and 22 being the highest resolution imagery.
To see it for yourself in Google Earth download this KMl file