First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic, which is the Mercator projection. It gives a broad overview of the subject without going into details. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with 'It', which is a pronoun and needs context. Paragraph 3 starts with 'However', which is a conjunction and shows a continuation of thought. Paragraph 4 starts with 'Thus', which also indicates a continuation. Therefore, they do not qualify as independent sentences.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it wraps up the discussion about the Mercator projection. It summarizes the impact of the projection by mentioning the debates it has caused. This follows the rule of Summary Style.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects with Paragraph 1 because it continues the idea of the Mercator projection. The phrase 'It presented' refers back to the Mercator projection. This follows the Noun Pronoun Rule.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects with Paragraph 2 because it adds more information about the projection. The word 'However' shows a contrast to the positive aspect mentioned in Paragraph 2. This follows the Contrast rule.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects with Paragraph 3 because it explains the result of the distortion mentioned in Paragraph 3. The word 'Thus' shows that the debates are a result of the distortion. This follows the Cause and Effect Relationship rule.