sono keisatsukan wa, kono machi no chizu ni totemo kuwashii deshou.

That police officer is probably very familiar with this town’s map.

Breakdown of sono keisatsukan wa, kono machi no chizu ni totemo kuwashii deshou.

• は: topic particle
• の: possessive case particle
• とても: very
• この: this

Questions & Answers about sono keisatsukan wa, kono machi no chizu ni totemo kuwashii deshou.

What does その mean here, and how is it different from この and あの?

その roughly means “that (near you / that one we’ve been talking about)”.

• この = this (near the speaker)
  
  • Example: この町 = this town (where I am / we are now)
• その = that (near the listener, or already known in the conversation)
  
  • その警察官 = that police officer (you know, the one we mentioned / the one near you)
• あの = that over there (far from both speaker and listener, or more distant / not directly involved)

In this sentence, その警察官 suggests:

• We both know which police officer we’re talking about, or
• The officer is “on your side” / near you, or
• The officer was mentioned earlier in the conversation.

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Why is there a は after 警察官? What does it do?

は is the topic marker.

• その警察官は = “As for that police officer,” / “That police officer…”

It tells you what the topic of the sentence is—what we’re talking about—before giving information about it.

So the structure is:

• その警察官は (topic: that police officer)
• この町の地図にとても詳しいでしょう (comment: is probably very familiar with the map of this town)

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What does この町の地図 literally mean, and what is the role of の?