This sightseeing heatmap is not very accurate but nonetheless gives an indication of popular photo spots. Select “Top spots” to displays markers for the most photographed small areas of the world. The heatmaps are based solely on the number of available Panoramio photos for an area: both the number of photos and the number of authors is taken into account.
Dark and Blue indicate few photos, Red indicates more, with Yellow indicating the largest number of photos geotagged.
Remember that popularity is often a self-fulfilling prophecy. Similar to the “Most Viewed” photos or articles that incite people to click and therefore become “most viewed” — the more people believe these are great spots to photograph and visit and photograph them, the more “popular” they become.