〜によって: means, cause, and a basis for variation
Read how によって after a noun can mark a method, a cause, or the factor across which something varies. Distinguish によっては when it singles out some possible cases.
Mark a method or means
新しい方法によって、作業時間を半分に減らしました。 means that a new method was used to cut the work time in half. Look before によって for what enabled the result.
によって often presents a means in formal or explanatory writing. It is not required for every everyday instrument, and で may be more natural in some contexts.
Connect a cause with its result
強風によって、午後の船は欠航になりました。 says that the afternoon ferry was canceled because of strong winds. によって can present a natural event or incident as the cause of a result.
Even when the predicate describes a result, the noun before によって may be a deliberately chosen method or an event or condition that caused the result. Use the wider context rather than deciding from the particle or predicate shape alone.
Show variation and single out some cases
読む人によって、この物語の解釈は変わります。 means that the interpretation of the story varies with the reader. The noun before によって supplies the factor across which the difference appears.
店によっては、予約が必要です。 says that reservations are required at some shops. によっては singles out possible cases and does not generalize the statement to every shop.
Quick check: Does 地域によっては、春にも雪が降ります。 say that it snows in spring in every region?
Show the answer and why
No. It says that this happens in some regions; は highlights a subset of the possible cases.