にわたって vs にかけて vs を通して

spans or extends across a period or range

It indicates that an event, state, or activity extends continuously across a long period, distance, or broad range of topics. It follows a noun expressing time, length, or scope, as in 長年にわたって, 多岐にわたり, and 広範囲にわたる研究. The にわたって and にわたり forms work adverbially, while にわたる, にわたった, and にわたっている can modify a noun or end a sentence as the predicate. It is formal and suits large scale spans in writing and speeches, and にわたる is normally written in hiragana for this meaning.

1. 彼かれの生涯しょうがいはほぼ１世紀せいきにわたった。

   His life spanned nearly a century.

2. 話は多岐にわたった。

   We talked about various topics.

spanning from one point to another

から〜にかけて expresses a span stretching from one point to another, such as a period of time or an area of the body or map. It attaches to two nouns in the pattern 5月から8月にかけて or 腰からひざにかけて. Unlike から〜まで, which marks clear start and end points, it presents the range as a broad, continuous zone and is common in formal descriptions of weather, history, and gradual change.

1. 雨あめがよく降ふるのは、５月がつから８月がつにかけてです。

   The months with the most rain are May, June, July and August.

2. その役場は１８９５年から１８９７年にかけて建てられました。

   The town hall was built between 1895 and 1897.

by way of; by means of an intermediary or medium

を通して expresses that an action happens by way of a person, group, activity, or medium, such as getting a job through a friend or learning about society through television. It follows a noun directly, and を通じて is an equivalent variant with the same meaning and usage. It is neutral and common in both conversation and writing.

1. 野球やきゅうを通とおしてたくさんのことを学まなべます。

   You can learn a lot by playing baseball.

2. 私はリーさんを通して彼と知り合いになった。

   I met him through Lee.