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Difficulty: MediumInferences from the Text

While early modern navigational charts—known as portolan charts—accurately mapped coastal outlines using magnetic compass bearings (rhumb lines) and dead reckoning, they lacked a unified mathematical projection accounting for the Earth's curvature. Consequently, navigators plotting straight-line courses across transoceanic distances accumulated systematic positional errors. Gerardus Mercator’s 1569 projection resolved this operational limitation not by depicting true geographic areas or shortest physical distances, but by mathematically distorting latitude spacing to ensure that lines of constant compass bearing appeared as straight lines on a flat plane. While this enabled transatlantic mariners to follow a single compass heading directly between two points, navigators charting polar routes found the projection increasingly impractical due to extreme areal distortion.

Based on the passage, which of the following statements regarding transatlantic navigators prior to the adoption of the Mercator projection is most strongly supported?

  1. A
    They frequently misidentified coastal topography because portolan charts failed to record accurate shoreline outlines.
  2. B
    They avoided plotting straight-line courses on portolan charts because they preferred calculating the true shortest physical distance between continents.
  3. They experienced cumulative positional discrepancies when attempting to navigate across oceans along straight lines drawn on their charts.Answer
  4. D
    They favored sailing polar routes where portolan charts did not suffer from the spherical distortion typical of open-ocean travel.
  5. E
    They relied on map projections that accurately preserved landmass area proportions at the expense of consistent directional bearings.

Answer

Transatlantic navigators prior to the Mercator projection experienced cumulative positional discrepancies when attempting to navigate across oceans along straight lines drawn on their charts.
The correct answer accurately synthesizes the passage's explicit statements: portolan charts lacked a mathematical projection for the Earth's curvature, which caused navigators who plotted straight-line transoceanic courses to accumulate systematic positional errors. Thus, sailing along straight lines on these charts resulted in cumulative positional deviations.

Step-by-Step Solution

1
Identify the relevant textual evidence concerning navigational practices prior to Mercator's 1569 projection.
The passage notes that portolan charts lacked a projection accounting for Earth's curvature, leading navigators who plotted straight-line transoceanic courses to accumulate systematic positional errors.
Establishing the specific textual facts regarding pre-Mercator navigation isolates the premise required for valid inference.
2
Synthesize the cause-and-effect relationship outlined in the text.
Following straight-line courses over oceanic expanses on unprojected charts directly produced accumulated positional inaccuracies.
Inference questions on the LSAT require strict adherence to the logical consequences entailed by the passage without introducing unstated assumptions.
3
Evaluate the choices to find the statement that precisely matches the synthesized relationship without introducing unwarranted scope or extreme qualifiers.
The statement describing cumulative positional discrepancies along charted straight lines accurately paraphrases the passage's entailment.
Eliminating options that contradict explicit facts or import unsupported claims confirms the unique validity of the correct inference.

Key Concept

Drawing strictly supported textual inferences from explicit cause-and-effect relationships in informational prose.
Estimated Time:1m 15s
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Topics

Inferences from the Text

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