https://en.wikipedia.org/wiki/JSON
JSON stands for Java Script Object Notification. Apple has used it instead of postscript, pdf or quadratic spline vector formats because they can code into it the smarts for the adjustable corners, numbers of sides, radius and star points. It maybe related to what Apple did inside TrueType fonts.
You can view it in a text editor but it looks like a a very long list of co-ordinates and geometric information, which Apple has obviously got Pages to parse and make sense of.
This could have been done as a pdf which would have been more compact, editable and portable but Apple doesn't get its own stated principles of smart design and hasn't for a very long time. It actually would make their own internal work easier, instead of all this proprietary nonsense that doesn't talk well with anything else.
If you want to access the actual library as a reference vector collection, drop everything from the Shapes collection onto a page or set of pages and print that to pdf. You'll be able to get at all the shapes in a vector editing program that can read pdfs.
Be prepared for less than stellar detailing when you get a close look at the vectors they are mostly just join the dots and relatively few intelligent curves. The maps are worst at this.
The OBVIOUS (but not to Apple) method to implement vector graphics was to make a way of retaining your own graphics and drawings and adding them to the library. Or simply to have all of these as drag and drop pdf collections which would have solved all the above problems in a natural macOS way. But then today's Apple seems to show a profound lack of comprehension of Macs and Maclike design principles.
