☰ Contents · Geography

Map projections and conventional signs

Lessons 5–6 · 2 lessons · P. Gulomov, H. Vahobov, P. Baratov, M. Mamatqulov. Geography (Physical Geography of Central Asia; Physical Geography of Uzbekistan), Grade 7. Revised and expanded 5th edition. “O‘qituvchi” Publishing House, Tashkent, 2017
5

Geographic maps and the idea of map projections

Textbook: pp. 12–14
GoalUnderstand why maps contain distortions and know the main kinds of map projections.
New words
map projection · xarita andazasi (proyeksiya)conformal (equal-angle) projection · teng burchakli andazaequal-area projection · teng maydonli andazaconic projection · konussimon andaza
Explanation

A globe is a reduced model of the Earth and keeps the shapes of continents and oceans almost exactly, but it cannot show small details. On a map the Earth’s curved surface is transferred onto a plane, so some places are stretched and others shrunk and distortions appear. To reduce these errors map projections are used, which are mathematical ways of putting a curved surface onto a plane. In a conformal (equal-angle) projection angles are kept as on the ground, so finding direction is easy, but areas and distances are distorted. In an equal-area projection areas are correct but shapes and angles are distorted; arbitrary projections have both errors but small ones. By the auxiliary surface used, projections are cylindrical, conic and azimuthal; maps of Central Asia and Uzbekistan are drawn in a conic projection.

Worked examples
An orange peel cannot be laid flat on a table in one piece without tearing or stretching; the same happens when the Earth’s surface is put on a map.
To compare the areas of states an equal-area map is preferable; for a sailor finding direction a conformal map is more convenient.
Class activity

“Orange experiment” (with a parent or teacher): peel an orange by hand, lay the pieces on a desk and discuss why gaps remain.

Practice
1
What is the main difference between a globe and a map?
2
Which kind of projection is needed to measure areas?
3
In which projection are the maps of Central Asia drawn?
4
Why can’t the Earth’s surface be put onto a plane without any error? Explain.