I submitted this answer after an answer was selected "correct".
(I've been researching this since it was first posted.)
PART 1 - MBTI Semantics - This section focuses on MBTI semantics to help understand the sentences.
S1: As an ISTJ, your primary mode of living is focused internally, where you take things in via your five senses in a literal, concrete fashion.
S2: Your secondary mode is external, where you deal with things rationally and logically.
S1 describes introverted sensing from the IS-J relationships:
S1.0: As an ISTJ,
S1.1: your primary mode of living [PERCEIVING] is focused internally [INTROVERT],
S1.2: where [where the prior MBTI stuff indicates that from your perceiving function...]
S1.3: you take things in [PERCEIVING] via your five senses in a literal, concrete fashion [SENSING].
S2 describes extraverted thinking from the I-TJ relationships:
S2.1: Your secondary mode [DECISIONS aka JUDGING] is external [EXTROVERT],
S2.2: where [where the prior MBTI stuff indicates that from your decision function...]
S2.3: you deal with things [DECISIONS/JUDGING] rationally and logically [THINKING].
Above, I've given a rough translation of 'where', retaining its 'abstract-place' relationship to both the prior and following clause:
- "where the prior MBTI stuff indicates that from your perceiving function...".
This could be reworded to include your original interpretation of 'where=meaning' while retaining the location function:
- "where the prior MBTI stuff means that from your perceiving function..."
I'm going to argue that the original sentences S1 and S2 are poorly written, attempting to create an odd compromise between clarity and conciseness; they do not contain enough information to be clear, yet they could be more concise. Both of the above sentences can be stated concisely in a single combined sentence I'll call S3:
- S3: As an ISTJ, you have (1) introverted sensing and (2) extraverted thinking.
This excludes some pseudo-semantic information; to really understand the "semantics" of the original sentences requires a broad understanding of MBTI theory-space. I'm not saying S3 is "better" than S1 or S2. Obviously, the original author didn't want such a dry definition-sounding introduction. But the end result is S1 and S2 are muddled.
Compare with the following directions: "Just go down that road until you see the fork in the road before Mrs. Smith's house, where you'll veer right and then take a left on the road between John and Kerry's land." The sentence is grammatically correct, but if you're just passing through the town, you don't know any more than you started. You cannot know the location of "where" (or the functional meaning of the sentence) without already-having (or acquiring) missing information. You need to know more about the map/model.
The following link is a pretty good explanation of the MBTI concepts of "introverted sensing", "extraverted thinking", and similar combinations.
PART 2 - Grammar
In S1 and S2, the word 'where' is functioning as a relative pronoun or relative adverb to refer to (abstract) places in both the prior and following clauses. This creates a non-restrictive relative clause (aka non-defining relative clause). But what place? I believe the author is trying to sum up a lot of the MBTI theory in two sentences to be concise. The author understands what this means, but it's not much help for the reader. The 'where' is referencing somewhere in the MBTI model-space from the prior clause and relating to the MBTI model-space in the next clause. The MBTI theory is multi-dimensional, while language is linear, so this style of explaining complex relationships is vague at best and misleading at worst. The sentences are simply poor style.
This "poor style" judgement of mine is relative. The question is, "who is the reader"? If we assume the reader to have a very high level of MBTI-knowledge, the sentences are fine. I think the sentences made perfect sense to the author (or someone that deeply understands the MBTI model) because all the gaps can be filled in. The 'abstract where' is partially in the prior sentence, but also external - in MBTI model-space.
Why does the use of 'where' make sense to native speakers?
Sentences like these seem to make sense intuitively to native language speakers, but they often don't understand “why”. There is not much literature I could find on the use of 'where' with sentential, non-defining parallel clauses. Most examples have more simple and clear antecedents like this: "I went to Paris, where I enjoyed the food."
I think 'where' works intuitively because of the directional words at the end of the clause. However, I don't think the antecedent of the "where" is only referring to such. The following sentences may give some insight:
- Fire shoots inwards, where it frizzles the gizzle. (OK)
- As a WXYZ, fire shoots inwards, where it frizzles the gizzle. (OK)
- Fire shoots inwards as a WXYZ, where it frizzles the gizzle. (LESS GOOD because the 'where' clause is separated from the location indicator 'inwards'.)
- Fire shoots fast, where it frizzles the gizzle. (BAD. 'fast' doesn't provide a location and abstract fire does not have a location. On the other hand, if someone were saying this and pointing to a burning chamber, it would be OK.)
- The fire shoots fast, where it frizzles the gizzle. (OK BUT MORE COMPLEX. The article 'the' indicates a particular fire. One would have to think, "The location of the fast-shooting fire frizzles the gizzle."
- Something moves somewhere, where it does something else. (OK. 'somewhere' provides a location.)
The “Random Idea English” blog has an excelllent article on non-defining relative clauses.
Also, see this very funny article called “Escaped Relatives” (warning: intended for native or fluent english speakers).
I think there is much more that could be said about this in terms of linguistics. There might be an opportunity here for a linguist to evaluate the use of "where" in non-restrictive relative clauses in which 'where' refers (at least in part) to some model-space outside of the immediate text.