Today I added a new connection called Pictographs, which has lead to some questions. I'll try to explain my reasoning:
- There's already a category called Rock Art; true, but categories only hold those sites which main feature is Rock Art; there also plenty of other sites that were inscribed for another reason but also hold some examples of rock art
- There's already a connection called Petroglyphs; true, but pictographs are something different (rock paintings instead of engravings)

I plan to follow this definition:
Petroglyphs are images created by removing part of a rock surface by incising, pecking, carving, and abrading. The term petroglyph should not be confused with pictograph, which is an image drawn or painted on a rock face. Both types of image belong to the wider and more general category of rock art.

I guess there's a thin line between these two types. Some of the Scandinavian Rock Art-sites look like paintings, but are actually petroglyphs (they are painted nowadays with red ink to make the engravings visible to visitors). Some sites both have petroglyphs and pictographs.