On the Earth, approximately how many kilometers on the surface are represented by one degree of latitude?

Introduction / Context:
Latitude and longitude coordinates are angular measurements, but in geography they are often converted into approximate distances on the Earths surface. For latitude in particular, there is a well known approximate relationship between one degree of latitude and distance along a meridian. This question tests your ability to recall that one degree of latitude corresponds to roughly 111 kilometers on the Earths surface, a value used widely in navigation and map calculations.

Given Data / Assumptions:

• The question is about one degree of latitude, not longitude.
• We assume the Earth is approximately spherical, with minor polar flattening ignored for this estimate.
• Options suggest several possible distances in kilometers.
• We focus on average distance along a meridian between two adjacent degrees of latitude.

Concept / Approach:
The total circumference of the Earth around a great circle is about 40,000 kilometers. A full circle contains 360 degrees. Therefore, if you divide 40,000 kilometers by 360, you obtain a value close to 111 kilometers per degree. This method works best for distances along meridians, which correspond to changes in latitude. Distances per degree of longitude vary with latitude, becoming smaller toward the poles, but latitude degrees remain almost constant in length. Thus, for general purposes, one degree of latitude is taken as approximately 111 kilometers.

Step-by-Step Solution:
Step 1: Recall the approximate circumference of the Earth as 40,000 kilometers. Step 2: Note that a full circle is 360 degrees, so you can find the approximate distance per degree by dividing 40,000 by 360. Step 3: Perform the approximate division: 40,000 km / 360 is roughly equal to about 111 km per degree. Step 4: Compare this value to the options given and identify 111 km as the closest match. Step 5: Select 111 km as the correct answer.

Verification / Alternative check:
Another way to confirm this is to recall standard geographic facts taught in school: many textbooks directly state that one degree of latitude equals around 111 kilometers and that one minute of latitude is approximately 1.85 kilometers, which is close to one nautical mile. These values are consistent and used in navigation and mapping around the world. Since the Earth is not a perfect sphere, the exact value varies slightly, but the approximation of 111 kilometers remains accurate enough for exam purposes.

Why Other Options Are Wrong:
321 km: This distance would be almost three times too large for a single degree and does not match the accepted value.
211 km: This is nearly double the correct distance and would cause large errors in any map calculations.
91 km: This is significantly smaller than the accepted value, and no standard reference assigns such a low figure to one degree of latitude.
51 km: This is less than half the correct value, again inconsistent with known Earth dimensions.

Common Pitfalls:
Students sometimes confuse the distance for one degree of latitude with other approximate values, such as the length of a minute of latitude or distances linked to time zones. Another pitfall is forgetting the simple circumference divided by 360 approach. To avoid mistakes, memorize the approximate equivalence that 1 degree of latitude equals about 111 kilometers and 1 minute of latitude equals about 1.85 kilometers. Keeping these two key numbers in mind will help you quickly answer many questions about geographic distance and coordinates.

Final Answer:
On the Earth, one degree of latitude corresponds to approximately 111 km on the surface.