Maps, Measurement, and Planet Earth Lesson 

Lesson Overview

• Earth's Shape and Structure
• Geographic Coordinates: Latitude and Longitude
• Using the North Star (Polaris) to Determine Latitude
• Topographic Maps and Contour Lines
• Calculating Gradient
• Maps, Measurement, and Planet Earth Assessment

Maps and measurements of Earth's features are essential for understanding geography and the planet's structure. In this lesson, we will explore Earth's true shape, the geographic coordinate system, how to use topographic maps, and methods for determining elevation and slope. Our goal is to develop a deeper understanding of Earth's surface and how geographers represent it in two-dimensional forms.

Earth's Shape and Structure

1. Earth's Shape: Oblate Spheroid

While Earth may seem spherical at first glance, it is actually an oblate spheroid, meaning it is slightly flattened at the poles and bulging at the equator. This shape results from the Earth's rotation. The centrifugal force from spinning causes the equator to bulge outward. The polar diameter is shorter than the equatorial diameter by about 43 kilometers.

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Maps, Measurement and Planet Earth 2

2. Evidence of Earth's Curvature

The curvature of the Earth is visible in several real-world scenarios, such as when a ship moves away from a coastline. As the ship recedes into the distance, the hull appears to "sink" below the horizon. This happens because the Earth's surface is curved, and the line of sight from the observer is eventually parallel to the Earth's surface, causing lower parts of distant objects to disappear first.

Example:

• When observing a ship sailing away, the hull disappears first, followed by the mast. This is not due to any irregularities in the ocean's surface but the result of Earth's curvature.

3. Earth's Spheres

Earth can be divided into four major spheres:

1. Lithosphere – Earth's solid outer layer, including landforms such as mountains, valleys, and the ocean floor.
2. Hydrosphere – All of Earth's water, including oceans, rivers, lakes, and groundwater.
3. Atmosphere – The layer of gases surrounding Earth, providing oxygen, protecting from solar radiation, and regulating climate.
4. Biosphere – All living organisms on Earth, including humans, animals, plants, and ecosystems.

Understanding these spheres is essential for interpreting geographic data. For instance, studying the hydrosphere might involve analyzing water bodies, while studying the lithosphere focuses on landforms and geology.

Geographic Coordinates: Latitude and Longitude

To pinpoint locations on Earth, we use the geographic coordinate system based on latitude and longitude.

1. Latitude

Latitude lines are imaginary horizontal lines that run parallel to the Equator, which is the baseline for measuring latitude at 0°. Latitude values range from 0° at the Equator to 90° at the poles, and they are classified as either North (N) or South (S).

2. Longitude

Longitude lines are vertical lines running from the North Pole to the South Pole, starting at the Prime Meridian (0° longitude), which runs through Greenwich, London. Longitude values range from 0° to 180° east and west of the Prime Meridian.

Together, latitude and longitude create a coordinate grid, enabling us to precisely locate any point on Earth.

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Maps and Measurements Pre-Assessment (Earth Science Regents)

Using the North Star (Polaris) to Determine Latitude

In the Northern Hemisphere, Polaris (the North Star) is a reliable reference for determining latitude. The altitude of Polaris (its angle above the horizon) equals the observer's latitude. For example, if Polaris is 40° above the horizon, the observer is at 40° N latitude.

Example:

• If you measure the altitude of Polaris at 60° above the horizon, your latitude is 60° N.

Topographic Maps and Contour Lines

Topographic maps represent three-dimensional terrain on a two-dimensional surface using contour lines. These lines connect points of equal elevation. The spacing between contour lines indicates the steepness of the terrain: closely spaced lines show steep areas, while widely spaced lines indicate gentle slopes.

1. Interpreting Contour Lines

• Closed loops with increasing values toward the center indicate hills or mountain peaks.
• Closed loops with decreasing values indicate depressions or valleys.
• V-shaped contour lines indicate a river or stream, with the V pointing upstream.

Contour Interval: The difference in elevation between consecutive contour lines is called the contour interval. It is usually stated in the map legend.

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Topographic Maps Review Quiz

Example: Topographic Map

Calculating Gradient

The gradient (also called slope) is the rate of elevation change over horizontal distance. It is calculated by dividing the change in elevation by the horizontal distance.

Formula:

Gradient = Horizontal distance/Elevation change​​

Example:

• If the elevation at point A is 300 meters and the elevation at point B is 100 meters, and the distance between them is 4 kilometers, the gradient is calculated as:

                               Gradient = 300−100​/4

= 200/4

​ = 50m/km

This means that for every kilometer traveled horizontally, the elevation changes by 50 meters.

Maps, Measurement, and Planet Earth Assessment

1. Latitude and Longitude: What is the approximate latitude and longitude of Paris, France?

1. Topographic Map Interpretation: On a map, you see a series of contour lines that form closed loops with increasing elevation. What do these loops represent?

1. Gradient Calculation: You measure a 2 km distance between two points on a hill. The elevation at point A is 500 m and at point B is 400 m. What is the gradient?

Answers:

1. Answer: Latitude 48° N, Longitude 2° E.
2. Answer: These represent mountain peaks.
3. Answer: 50m/km.