Other users got 15GB, 67GB, 72GB of free storage, so it looks like Google's bonus is not the same for everyone. It's not clear how you can obtain the Google Maps Views bonus, but I assume it could be influenced by the number of photos and panoramic images you add to Google Maps Views, the number of photos approved to be displayed in Google Maps and their popularity.
All the photos you've publicly shared in Google+ and they're also tagged with a location and have the "Show location" setting checked are automatically added to Google Maps Views and some of them are added to Google Maps. "Google Maps tries to algorithmically choose a variety of interesting, high-quality photos that give you a sense of place. To keep the focus on the location, photos that have people in them are typically not chosen," explains Google.
You can check your storage here: mouse over the chart to see the breakdown.
Update: Stephen Shankland from CNet found a post from the Panoramio group which says that Panoramio users will receive bonus Google Drive storage: "We will provide an easy way for you to migrate all your Panoramio photos, their metadata, and their viewcounts to Views. Your photos will be saved into public albums in Google+ and we will provide you a Google Drive storage bonus to cover the additional data usage."