12th Standard Geography — Map Projection Online Test
Unit 10 of 12th Geography explains map projection, the representation of the globe's graticule on a flat sheet. It classifies projections by method of construction, developable surface, properties and light source, and shows how to construct cylindrical equal area, cylindrical equi-distant and polar zenithal equal area and equi-distant projections.
Study this chapter
About Map Projection
Medium ~50 min study
Map Projection is Unit 10 of the Tamil Nadu State Board Class 12 Geography book and part of its Practical Geography section. A map projection represents the latitudes and longitudes of the globe on a flat sheet of paper, and the network so formed is called the graticule. Because a three-dimensional surface is shown on a two-dimensional plane, some property such as shape, size, area or direction is always distorted.
The lesson first classifies projections by method of construction, developable surface, properties and position of light source. It then gives step-by-step constructions of four projections with reduced earth radii and 30 degree intervals.
The book exercise has only drawing tasks and no printed multiple choice questions, so this page offers additional one mark questions written from the lesson, each with a short explanation.
What you'll learn
- Define map projection and graticule.
- Classify projections by method of construction, developable surface, properties and light source.
- Distinguish normal, transverse and oblique cylindrical projections and tangent and secant conical projections.
- Name the aspects of zenithal projection and the region each type suits.
- List the properties of the four projections constructed in the lesson.
- Construct cylindrical and polar zenithal projections with a given radius and interval.
Before you start
- Latitudes, longitudes, the equator and the poles on a globe.
- Use of a scale, compass and protractor to draw circles and angles.
- Simple division such as 360/30 and 180/30.
Topics covered in this chapter
Map Projection explained
What this lesson covers
Classification of map projections
Perspective projections use the shadow of an illuminated globe cast on a developable surface; non-perspective projections assume the surface and use mathematical calculations. By developable surface there are cylindrical, conical and zenithal projections. Cylindrical projections may be normal (tangent to the equator), transverse (tangent to a meridian) or oblique. Conical projections may be tangent or secant and suit middle latitudes. Zenithal projections have equatorial, oblique and polar aspects and suit polar areas.
Properties and light source
Equal area projections are homolographic, true shape projections are orthomorphic, and true scale projections keep correct scale only along some parallels or meridians. By light source there are gnomonic (centre of globe), stereographic (periphery) and orthographic (infinity) projections.
Constructions
The lesson constructs the Cylindrical Equal Area projection of J.H. Lambert (1772), the Cylindrical Equi-distant projection of Marinus of Tyre, and the Polar Zenithal Equal Area and Polar Zenithal Equi-distant projections, listing the properties of each.
Common mistakes to avoid
- Calling Cassini a normal cylindrical projection. It is transverse, tangent to a meridian.
- Using conical projection for polar areas. Conical suits middle latitudes; zenithal suits polar areas.
- Mixing up homolographic (equal area) and orthomorphic (true shape).
- Placing the light source of the gnomonic projection at the periphery. It is at the centre of the globe.
- Thinking any projection keeps true scale everywhere. Scale is true only along some parallels or meridians.
- Dividing the central meridian into 12 parts. The meridian spans 180 degrees, so a 30 degree interval gives 6 parts.
Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.
Frequently asked questions
What is a map projection?
A map projection is the representation of the latitudes and longitudes of the globe on a flat sheet of paper. It is a mathematical expression in which the three-dimensional surface of the earth is shown on a two-dimensional plane, so it distorts shape, size, area or direction.
What is the difference between perspective and non-perspective projections?
Perspective projections are made with the help of the shadow cast from an illuminated globe on to a developable surface. In non-perspective projections the developable surface is only assumed to cover the globe, and the projection is constructed with mathematical calculations.
Why is cylindrical projection suitable for equatorial regions?
In a cylindrical projection the length of the equator on the cylinder is equal to the length of the equator on the globe. Parallels and meridians are straight lines, so the equatorial regions are shown well.
What are tangent and secant conical projections?
In a tangent conical projection the cone touches the globe along only one parallel. In a secant conical projection the cone is not big enough to cover the curvature of the earth, so it intersects the earth twice, at two standard parallels.
How are projections classified by the position of light source?
Gnomonic projection has the light at the centre of the globe. Stereographic projection has it at the periphery, diametrically opposite the point where the developable surface touches the globe. Orthographic projection has it at infinity, opposite that point.
Why is the Cylindrical Equi-distant projection used for general purposes only?
The Cylindrical Equi-distant projection is neither equal area nor orthomorphic. Its scale is true only along the equator, and the distance between parallels and meridians remains the same throughout, so its maps are used for general purposes only.
Last updated 19 October 2026