I am trying to get an idea of the average most recent imagery dates of Madagascar in Google Earth. Rather than zooming in and looking at the lower corner for the imagery date, what is the best way to find out how much of the country is covered by imagery from a given year?
If you are referring to satellite imagery then I suggest using https://earthexplorer.usgs.gov/ instead of Google Earth. EarthExplorer gives access to quite a few different satellites and the imagery. Satellite imagery from Landsat 7 or 8 may be useful for you. Each satellite makes a complete orbit every 99 minutes, and does roughly 14 full orbits each day, while crossing every point on Earth once every 16 days. The dates for the images are given in the metadata for any of the satellite images. So that could help you find how much is covered in imagery through the year. On a side note I do not know how much of Madagascar is covered in each path, so you may need multiple images from each day to find the full coverage.
Thought I'd add my two cents -- see my answer here for a way to get the imagery data from Google Earth. If you select View and then Historical Imagery, a slider will appear that will allow you to determine the date and source of layers.