Mapping is a relatively simple way of capturing what you can 'see' about a system.
Systems thinking is about thought--the collective noun--and how thought as a system operates as an whole...including how thought becomes activity and data. . After appreciating thought and the related system dynamics one can choose to act on a more informed basis. But methodologically, is system thinking just about mapping?
Mapping is simply a very handy way to represent the system, to help understand it more easily and evaluate it more effectively. Mapping is just a form of modeling a system, an approximation to express an idea of what the reality might be.... Systems by definition are not undivided wholes; but rather a mix and match of what being called both collaborative and parasitic processes, the nature of which finds a balance within specific boundary conditions, where the whole with its emergent behavior is greater than the relative sum of its parts, the processes.
Mapping is about developing some simplifying models that can be used for thinking about a situation. And there usually many different models that can represent various perspectives. And maps are isomorphic with representations as matrices and algebra. An important thing to remember about diagramming / mapping in terms of nodes and connections is the underlying simplifying assumption that parameters are lumped - that is expressible in terms of nodes. A 'Lumped Parameter' formulation is a modeling convention of convenience - it makes the drawing and the math simpler. So too, the chosen parameters are simplifying selections from amongst the spate of things actually going on. It's hard to think of guidelines in Systems Science and Systems Thinking which are not at some level expressible as diagrams.
Mapping is a relatively simple way of capturing what you can 'see' about a system - the thinking element builds on this and involves applying what you 'know/perceive' about the system that cannot be shown in the map, and also identifying areas where there are things that you don't or can't 'know/perceive' - it's being able to define the gaps in the map where the logic is changed by the environment in which an individual or group operates.
Predicting the impact of the change in a system is more difficult. Changing a step within the mapped system is relatively easy but predicting the impact of that change on the system, without an understanding of what the map doesn't or can't show, is far more difficult. Using 'mapping' as a gerund does not say much about how it relates to System Thinking (ST). However, when the term is used as a verb 'to map' then immediately the question 'what' - what is being mapped - becomes relevant. This in turn leads to questions about boundary, perceived reality etc., which are all very relevant to ST.
So 'mapping' is too general to try to find out how this activity is used when talking about ST and ST methodologies, but mapping is a necessary step to simplify what you can “see” about the system, and from there, the systematic approaches can be taken for complex problem solving and business management.