البوصلة في حقيبة الظهر.

A careful Modern Standard Arabic pronunciation is:

al-būṣlatu fī ḥaqībati aẓ-ẓahri

A few notes:

• البوصلة = al-būṣlatu
• في = fī
• حقيبة = ḥaqībatu / ḥaqībati depending on grammar
• الظهر is pronounced aẓ-ẓahr, not al-ẓahr, because ظ is a sun letter, so the l sound of ال assimilates.

In normal speech, many speakers do not fully pronounce case endings, so you may hear something closer to:

al-būṣla fī ḥaqībat aẓ-ẓahr

Because in Arabic, the present-tense to be is usually omitted.

So:

البوصلة في حقيبة الظهر
literally looks like: the compass in the backpack

but it means:

The compass is in the backpack.

This is completely normal in Arabic nominal sentences. If you wanted the past tense, you would use a form of كان:

• كانت البوصلة في حقيبة الظهر = The compass was in the backpack

It is a nominal sentence in Arabic.

Its two main parts are:

• البوصلة — the topic/subject (the compass)
• في حقيبة الظهر — the predicate/comment (in the backpack)

So the sentence structure is:

subject + prepositional phrase

This is a very common Arabic pattern for location sentences.

في is a preposition meaning in or inside.

So:

• في البيت = in the house
• في السيارة = in the car
• في حقيبة الظهر = in the backpack

Because في is a preposition, the noun after it goes into the genitive case in fully vowelled Arabic.

Because حقيبة الظهر is an iḍāfa construction, often called a construct phrase.

In an iḍāfa:

• the first noun does not take الـ
• the second noun can make the whole phrase definite

So:

• حقيبة ظهر = a backpack
• حقيبة الظهر = the backpack

Literally, it is something like bag of the back, but idiomatically it means backpack.

In an iḍāfa, the definiteness of the whole phrase is determined by the last noun.

Here:

• الظهر = the back (definite)
• therefore حقيبة الظهر becomes definite as a whole

This is a key rule in Arabic grammar:

• كتاب طالب = a student’s book / a book of a student
• كتاب الطالب = the student’s book

The same logic applies here.

الظهر literally means the back.

So حقيبة الظهر literally means the bag of the back, which is the Arabic way to say backpack.

Arabic often builds vocabulary this way: a literal noun combination becomes the normal name of an object.

So yes, the phrase is idiomatic, but the literal meaning still helps you understand its structure.

That final letter is taa marbūṭa (ة).

When a word stands alone, it is usually pronounced like -a:

• حقيبة = ḥaqība

But when the word is in an iḍāfa construction or when full case endings are pronounced, the ة is heard as t:

• حقيبة الظهر = ḥaqībat aẓ-ẓahr
• fully inflected: ḥaqībatu / ḥaqībati ...

So learners often first see حقيبة and expect ḥaqība, but in this phrase they hear ḥaqībat.... That is normal.

Because ظ is a sun letter.

With sun letters, the l of الـ is not pronounced separately. Instead, the following consonant is doubled.

So:

• written: الظهر
• pronounced: aẓ-ẓahr

Other examples:

• الشمس → ash-shams
• النور → an-nūr
• الطالب → aṭ-ṭālib

This is pronunciation only; the spelling still keeps الـ.

In fully vowelled MSA, the sentence is:

البوصلةُ في حقيبةِ الظهرِ

Here is why:

• البوصلةُ is the subject of the nominal sentence, so it is nominative: -u
• حقيبةِ comes after the preposition في, so it is genitive: -i
• الظهرِ is also genitive because it is the second term of the iḍāfa

So the full grammatical reading is:

al-būṣlatu fī ḥaqībati aẓ-ẓahri

In ordinary unvowelled writing, these short vowels are usually not written.

Yes, بوصلة is grammatically feminine.

A big clue is the ending ة.

That matters for agreement in other sentences. For example:

• البوصلة جديدة = The compass is new
• هذه البوصلة = This compass

So if you later use adjectives, pronouns, or demonstratives with بوصلة, they should usually be feminine.

Sometimes, yes, but the given order is the most neutral and straightforward:

البوصلة في حقيبة الظهر

If you move the prepositional phrase to the front, you change the emphasis:

• في حقيبة الظهر البوصلة — possible in special contexts, but not the most natural basic wording
• في حقيبة الظهر بوصلة — more like There is a compass in the backpack

So for a beginner, the best default is to keep the original order when you mean The compass is in the backpack.