Chapter 4: Map Projections| Class 11 Geography Practical Work

The Earth is a 3D sphere, but maps need to be 2D. Map projections are mathematical transformations that convert the curved Earth’s surface to a flat map, though this inevitably involves some distortion.

In this article, we will look into the topic of Map Projections in detail.

Chapter 4: Map Projections| Class 11 Geography Practical Work

Map Projections

Map projection is a method used to represent the spherical grid of latitude and longitude on a flat surface. It involves transforming the network of parallels and meridians onto a two-dimensional plane. While the Earth is not flat but rather geoid in shape, resembling a sphere, a globe serves as an accurate model of the Earth. On a globe, the continents, oceans, directions, and distances are accurately depicted, thanks to its spherical shape. The globe is divided by lines of latitude and longitude, with horizontal lines representing parallels of latitude and vertical lines representing meridians of longitude. This grid, known as the graticule, aids in map drawing. Projection involves the process of transferring this graticule onto a flat surface.

However, despite its accuracy, a globe has several limitations. It is costly, not easily portable, and cannot display minor details effectively. Additionally, the meridians appear as semi-circles and the parallels as circles on a globe. When transferred onto a flat surface through projection, these lines become either intersecting straight lines or curved lines.

Need for Map Projections

The Earth is a sphere, but maps are flat. To transfer the 3D surface of the Earth onto a 2D map, we need to use a map projection. A map projection is a mathematical transformation that converts the curved surface of the Earth to a flat surface. This is necessary because it’s impossible to represent the entire curved surface of the Earth accurately on a flat map without some distortion. Map projections help us to create flat maps that are useful for navigation, planning, and analysis, even though they involve some distortion.

Elements of Map Projections

a. Reduced Earth: The concept of a “reduced earth” involves representing the Earth’s model on a flat surface with a scaled-down version of its dimensions. This model should ideally resemble a spheroid, with the length of the polar diameter shorter than the equatorial diameter. The network of latitude and longitude lines, known as the graticule, can then be transferred onto this model.

b. Parallels of Latitude: Parallels of latitude are circles that encircle the Earth parallel to the equator, maintaining a consistent distance from the poles. Each parallel lies entirely within its own plane, perpendicular to the Earth’s axis. While these parallels are not uniform in length, they range from a point at each pole to the circumference of the Earth at the equator. They are identified and marked as latitudes ranging from 0º to 90º, both north and south.

c. Meridians of Longitude: Meridians of longitude are semi-circular lines drawn from one pole to the other in a north-south direction. Each meridian lies wholly within its own plane, intersecting at right angles along the Earth’s axis. While there is no distinct central meridian, the meridian of Greenwich is commonly chosen as the reference point, marked as 0° longitude. This reference meridian is used as a basis to delineate all other longitudes.

d. Global Properties: When creating a map projection, it is essential to preserve certain fundamental properties of the Earth’s surface. These properties include: (i) Maintaining accurate distances between any given points within a region; (ii) Preserving the shape of geographical features on the map; (iii) Ensuring precise representation of the size or area of regions; (iv) Consistently depicting the direction from one point within a region to another.

Classification of Map Projections

Drawing Techniques

Map projections can be classified based on the method of construction into perspective, non-perspective, and conventional or mathematical projections. Perspective projections involve the use of a light source to project the image of latitude and longitude lines from a globe onto a flat surface. Non-perspective projections are created without the need for a light source or casting shadows, typically on surfaces that can be flattened. Mathematical or conventional projections are derived through mathematical computations and formulas, with little relation to the projected image.

Developable Surface

Map projections can also be categorized based on the type of surface onto which the latitude and longitude network is projected. Developable surfaces are those that can be flattened without distortion, while non-developable surfaces cannot be flattened without distortion. Cylindrical projections are created by wrapping a paper cylinder around the globe, projecting the graticule network onto it, and then cutting it open to obtain a flat sheet. Conical projections involve wrapping a cone around the globe and projecting the network onto it before cutting it open to produce a flat sheet. Zenithal projections are directly obtained on a flat surface by touching the plane to the globe at a point and projecting the graticule onto it. These projections can be normal, oblique, or polar depending on the position of the plane touching the globe.

Global Properties

Map projections are also classified based on their ability to preserve certain global properties such as area, shape, direction, and distance. Equal area projections accurately represent the areas of different parts of the Earth. Orthomorphic or true-shape projections maintain the shapes of various areas correctly, often at the expense of area accuracy. Azimuthal or true-bearing projections accurately represent the direction of all points from the center. Equi-distant or true-scale projections maintain accurate distance or scale, although not consistently throughout the map.

Source of Light

Projections can be classified based on the location of the light source used in their construction. Gnomonic projections are created with the light source at the center of the globe. Stereographic projections are drawn with the light source placed at the periphery of the globe, diametrically opposite to the point where the plane surface touches the globe. Orthographic projections involve placing the light source at infinity from the globe, opposite to the point of contact with the plane surface.

Constructing Some Selected Projections

Conical Projection with one Standard Parallel

• A conical projection is created by projecting the graticule of a globe onto a developable cone, touching the globe along a standard parallel.
• The standard parallel is chosen, such as 40º N, and parallels above and below it are distorted in length.
• To construct this projection for a given area, such as 10º N to 70º N latitude and 10º E to 130º E longitudes, with a scale of 1:250,000,000 and 10º intervals:
  1. Draw a circle or quadrant representing the cone’s base with the appropriate standard parallel marked.
  2. Extend tangents from points on the circle to form the cone touching the globe at the standard parallel.
  3. Use the arc distance between parallels to draw semicircles on the cone’s surface.
  4. Draw perpendiculars from the apex of the cone to the base to establish the central meridian and mark the standard parallel.
  5. Draw other parallels and meridians based on distances and intervals.
• This projection preserves certain properties:
  • All parallels are arcs of concentric circles and equally spaced.
  • Meridians are straight lines converging at the pole and intersecting parallels at right angles.
  • Scale is true along meridians but exaggerated away from the standard parallel.
  • Meridians become closer towards the pole.
• However, it has limitations such as extreme distortion in the hemisphere opposite the standard parallel.

Cylindrical Equal Area Projection

• This projection, also known as Lambert’s projection, is derived by projecting the globe’s surface with parallel rays onto a cylinder touching it at the equator.
• Parallels and meridians are projected as straight lines intersecting at right angles, with the pole represented as a parallel equal to the equator.
• To construct this projection for a world map with a scale of 1:300,000,000 and 15º intervals:
  1. Draw a circle representing the cylinder’s base.
  2. Divide the equator’s length into equal parts, then extend these divisions as parallels.
  3. Draw perpendiculars from the equator to represent meridians.
• This projection preserves:
  • Straight lines intersecting at right angles.
  • Equal length of parallels and meridians.
• However, it has limitations such as increased distortion towards the poles.

Mercator’s Projection

• Developed by Gerardus Mercator in 1569, this orthomorphic projection maintains correct shape but distorts size.
• Parallels and meridians are straight lines intersecting at right angles, with spacing increasing towards the pole.
• To construct this projection for a world map with a scale of 1:250,000,000 and 15º intervals:
  1. Draw a line representing the equator and divide it into equal parts.
  2. Calculate distances for each latitude based on intervals and draw parallels and meridians accordingly.
• Properties include straight parallels and meridians, with correct shape but increased distortion towards the poles.
• Limitations include exaggerated scale in high latitudes and infinite representation of the poles.
• Uses include world maps and navigation purposes due to its suitability for showing sea and air routes.

Limitations of Map Projections

No single map projection can accurately represent the entire curved surface of the Earth on a flat map without some distortion. All map projections involve trade-offs and compromises. Depending on the projection used, different properties like area, shape, distance or direction may be distorted.

For example, the Mercator projection is good for navigation as it preserves shapes and directions, but it greatly exaggerates the size of landmasses at higher latitudes. The Peters projection is an area-preserving projection, but it severely distorts the shapes of landmasses.

Mapmakers have to carefully choose the projection that best suits the intended purpose of the map, understanding that no projection can be perfect. Awareness of a projection’s limitations and strengths is important when interpreting and using maps.

Conclusion – Class 11 Geography Chapter 4: Map Projections

No single map projection can accurately represent the entire Earth without distortion. Mapmakers must choose the projection that best suits the map’s purpose, while understanding its limitations. Awareness of a projection’s strengths and weaknesses is key when interpreting and using maps.

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FAQs on Class 11 Geography Chapter 4: Map Projections

Why are map projections necessary?

Map projections are necessary because it is impossible to accurately represent the 3D curved surface of the Earth on a 2D flat map without some distortion. Map projections allow us to create useful flat maps for navigation, planning, and analysis.

What are the three main properties of map projections?

The three main properties of map projections are:

• Equivalence: Preserving the relative size of different areas
• Conformality: Preserving the shape of small areas
• Equidistance: Preserving accurate distances from the map center to other locations

What are the main types of map projections?

The main types of map projections are:

• Cylindrical projections
• Conical projections
• Zenithal (azimuthal) projections

What are map projections?

Map projections are methods used to represent the Earth’s curved surface on a flat map.

Why are there different types of map projections?

Different projections exist because it’s impossible to accurately represent the Earth’s surface in two dimensions without distortion, leading to various projection methods suited for different purposes.