Map Projections | Class 11 Geography Notes

Mercator's Projection

Mercator's projection was developed by Dutch cartographer Gerardus Mercator in 1569. It is an orthomorphic projection based on mathematical formulas that preserve the correct shape of areas, making it highly useful for navigation. In this projection, the distance between parallels increases towards the poles. Like cylindrical projections, the parallels and meridians intersect at right angles. A key feature is that a straight line joining any two points on this map represents a constant compass bearing, called a Loxodrome or Rhumb line, which is very useful for navigation.

Example: Draw a Mercator's projection for the world map at a scale of 1:250,000,000 with 15° intervals.

Calculation:

• Radius of reduced earth R = 640,000,000 / 250,000,000 = 1 inch
• Length of equator = 2πR = (1 × 22 × 2) / 7 = 6.28 inches
• Interval along equator = (6.28 × 15°) / 360° = 0.26 inches

Distances for latitudes are calculated using a table of values increasing with latitude (e.g., 15° = 0.265 inch, 30° = 0.549 inch, up to 75° = 2.027 inches).

Properties: 1. Parallels and meridians are straight lines intersecting at right angles. 2. All parallels have the same length equal to the equator. 3. Meridians have equal spacing but are longer than on the globe. 4. Spacing between parallels increases towards poles. 5. Scale is true along the equator but distorted elsewhere. 6. Shape is preserved near equator but distorted at higher latitudes. 7. It is an azimuthal and orthomorphic projection.

Limitations:

• Scale exaggeration near poles causes size distortion (e.g., Greenland appears as large as USA).
• Poles cannot be shown because 90° parallels and meridians are infinite.

Uses:

• Widely used for world maps and atlases.
• Very useful for navigation, showing sea and air routes.
• Suitable for mapping drainage patterns, ocean currents, temperature, winds, rainfall, and other weather elements.

📊 Diagram: Figure 4.5 Mercator's Projection; Figure 4.6 Straight lines are Laxodromes or Rhumb lines and Dotted lines are great circles

🧪 Activity: Draw a Mercator Projection for the world map with R.F. 1:400,000,000 and 20° intervals.

🔗 Connection: Leads to exercises and activities to reinforce understanding of map projections.

Table on page 10 (6×2)