Microsoft's documentation is incredibly confusing or lacking in showing us how to generate a code structure / Code Map.
On visualstudio.com, in the "Compare Visual Studio 2015 Offerings" table, under Architecture and Modeling, it is shown that "Visualize solutions with Dependency Graphs and Code Maps" is supported in Visual Studio Community.
Old examples show that Code Maps are under the Architecture Explorer tab, but I don't have that tab in my VS. I also tried searching for Code Maps in Quick Launch, and got nothing.
The only thing I can do is go to File > New > File and make a new Directed Graph Document (.dgml). I can drag in classes to it, but that's not a generated diagram, it's a new blank one.
PS: The same happens for Visual Studio Enterprise 2015, not just Community 2015.
[EDIT] Apparently there IS an Architecture tab in VS Enterprise 2015. I was trying something called "Blend for Visual Studio Enterprise 2015" which seems to just be Visual Studio Community 2015... Great stuff.
You can't create Code Maps with VS 2015 Community or Professional. You need Enterprise to create them. They can be viewed in the Community or Professional Edition, after they have been created with VS 2015 Enterprise.
This is documented in Compare Visual Studio 2015 Offerings page. If you look at the "Architecture and Modeling" section you will see that in the Community and Professional columns Code Map has footnote no. 3. It says: "Read-Only diagrams".