This document discusses different types of map projections. It begins by defining map projection as a systematic drawing of parallels and meridians on a plane surface that corresponds to locations on Earth. It notes that all projections necessarily distort the surface in some way. Projections are classified based on their construction method, development surface, preserved properties, and position of the light source. Common projection types discussed include cylindrical, conic, azimuthal, Mercator, sinusoidal, and polyconic. The key properties and uses of each type are outlined. The document emphasizes that the purpose of the map determines the best projection to use.
2. Map Projection: Meaning and use
• Map projection is a systematic drawing of parallel of latitudes and meridians
of longitude on a plane surface for the whole earth or a part of it on a certain
scale so that any point on the earth surface may correspond to that on the
drawing.
• Maps cannot be created without map projections. All map projections
necessarily distort the surface in some fashion.
• Depending on the purpose of the map, some distortions are acceptable and
others are not; therefore, different map projections exist in order to preserve
some properties of the sphere-like body at the expense of other properties.
• There is no limit to the number of possible map projections
3. Classification of Map Projections
Map projections are classified on the
following criteria:
• Method of construction
• Development surface used
• Projection properties
• Position of light source
4. Method of Construction
The term map projection implies projecting the graticule of the earth onto a flat surface with the
help of shadow cast. However, not all of the map projections are developed in this manner.
Some projections are developed using mathematical calculations only. Given below are the
projections that are based on the method of construction:
• Perspective Projections : These projections are made with the help of shadow cast from an
illuminated globe on to a developable surface
• Non Perspective Projections :These projections do not use shadow cast from an illuminated
globe on to a developable surface. A developable surface is only assumed to be covering the
globe and the construction of projections is done using mathematical calculations.
5. Development Surface
Projection transforms the coordinates of earth on
to a surface that can be flattened to a plane
without distortion (shearing or stretching). Such a
surface is called a developable surface. The three
basic projections are based on the types of
developable surface and are introduced below:
• 1. Cylindrical Projection
• 2. Conic Projection
• 3. Azimuthal/Zenithal Projection
7. Projection Properties
According to properties map projections can be classified as:
• Equal area projection: Also known as homolographic projections.
The areas of different parts of earth are correctly represented by
such projections.
• True shape projection: Also known as orthomorphic projections.
The shapes of different parts of earth are correctly represented on
these projections.
• True scale or equidistant projections: Projections that maintain
correct scale are called true scale projections. However, no
projection can maintain the correct scale throughout. Correct scale
can only be maintained along some parallel or meridian.
9. Position of Light Source
Placing light source illuminating the globe at different positions
results in the development of different projections. These
projections are:
• Gnomonic projection: when the source of light is placed at
the centre of the globe
• Stereographic Projection: when the source of light is placed
at the periphery of the globe, diametrically opposite to the
point at which developable surface touches the globe
• Orthographic Projection: when the source of light is placed at
infinity from the globe opposite to the point at which
developable surface touches the globe
12. Simple Cylindrical Projection
Let us draw a network of Simple cylindrical Projection for the whole globe on
the scale of 1: 400,000,000 spacing meridians and parallels at 30º interval
Calculations
14. Steps of Constrution:
• Draw a line AB, 9.975 cm long to represent the equator. The equator is a circle on
the globe and is subtended by 360º.
• Since the meridians are to be drawn at an interval of 30º divide AB into 360/30 or
12 equal parts.
• The length of a meridian is equal to half the length of the equator i.e. 9.975/2 or
4.987 cm.
• To draw meridians, erect perpendiculars on the points of divisions of AB. Take
these perpendiculars equal to the length specified for a meridian and keep half of
their length on either side of the equator.
• A meridian on a globe is subtended by 180º. Since the parallels are to be drawn at
an interval of 30º, divide the central meridian into 180/30 i.e. 6 parts.
• Through these points of divisions draw lines parallel to the equator. These lines will
be parallels of latitude. Mark the equator and the central meridian with 0º and the
parallels and other meridians. EFGH is the required graticule.
15. Conical Projection
Let us draw a graticule on simple conical projection with one standard parallel on the scale of
1: 180,000,000 for the area extending from the equator to 90º N latitude and from 60º W
longitude to 100º E longitude with parallels spaced at 15º interval, meridians at 20º, and
standard parallel 45º N.
Calculations:
16. Steps of construction
• Draw a circle with a radius of 3.527 cm that represents the
globe. Let NS be the polar diameter and WE be the equatorial
diameter which intersect each other at right angles at O.
• To draw the standard parallel 45º N, draw OP making an angle
of 45º with OE.
• Draw QP tangent to OP and extend ON to meet PQ at point Q.
• Draw OA making an angle equal to the parallel interval i.e. 15º
with OE.
18. Azimuthal Projection
Let us draw Polar zenithal equal area projection for the northern hemisphere
on the scale of 1: 200,000,000 spacing parallels at 15° interval and meridians
at 30° interval.
Calculations:
19. Steps of construction:
• Draw a circle with radius equal to 3.175 cm representing a globe. Let NS and WE
be the polar and equatorial diameter respectively which intersect each other at right
angles at O, the centre of the circle.
• Draw radii Oa, Ob, Oc, Od, and Oe making angles of 15°, 30°, 45°, 60° and 75°
respectively with OE. Join Ne, Nd, Nc, Nb, Na and NE by straight lines.
• With radius equal to Ne, and N’ as centre draw a circle. This circle represents 75°
parallel. Similarly with centre N’ and radii equal to Nd, Nc, Nb, Na and NE draw
circles to represent the parallels of 60°, 45°, 30°, 15° and 0° respectively.
• Draw straight lines AB and CD intersecting each other at the centre i.e. point N.
• Radius N’B represents 0° meridian, N’A 180° meridian, N’D 90° E meridian and
N’C 90° W meridian.
• Using protractor, draw other radii at 30° interval to represent other meridians
21. Selection of Map Projection
• Considering the purpose of the map is important while
choosing the map projection. If a map has a specific
purpose, one may need to preserve a certain property such
as shape, area or direction
• On the basis of the property preserved, maps can be
categorized as following
a. Maps that preserve shapes.
b. Maps that preserve area
c. Maps that preserve scale
d. Maps that preserve direction
22. Maps that preserve shapes
Used for showing local directions and
representing the shapes of the features. Such
maps include:
• Topographic and cadastral maps.
• Navigation charts (for plotting course bearings
and wind direction).
• Civil engineering maps and military maps.
• Weather maps (for showing the local direction
in which weather systems are moving).
23. Maps that preserve area
The size of any area on the map is in true proportion to
its size on the earth. Such projections can be used to
show
• Density of an attribute e.g. population density with
dots
• Spatial extent of a categorical attribute e.g. land use
maps
• Quantitative attributes by area e.g. Gross Domestic
Product by country
• World political maps to correct popular misconceptions
about the relative sizes of countries.
24. Maps that preserve scale
Preserves true scale from a single point to all other
points on the map. The maps that use this property
include:
• Maps of airline distances from a single city to several
other cities
• Seismic maps showing distances from the epicenter
of an earthquake
• Maps used to calculate ranges; for example, the
cruising ranges of airplanes or the habitats of animal
species
25. Maps that preserve direction
On any Azimuthal projection, all azimuths, or
directions, are true from a single specified
point to all other points on the map. On a
conformal projection, directions are locally
true, but are distorted with distance.
28. Properties of Cylindrical Projection
• Parallels and meridians are straight lines
• The meridians intersect parallels at right angles
• The distance between parallels decrease toward the poles but meridians are
equally spaced
• The length of the equator on this projection is same as that on globe but other
parallels are longer than corresponding parallels on globe. So, the scale is true
along the equator but is exaggerated along other parallels
• Shape and scale distortions increase near points 90 degrees from the central
line resulting in vertical exaggeration of Equatorial regions with compression
of regions in middle latitudes
• Despite the shape distortion in some portions of a world map, this projection
is well suited for equal-area mapping of regions which are predominantly
north-south in extent, which have an oblique central line, or which lie near the
Equator.
29.
30.
31. Properties of Azimuthal Projection
• The pole is a point forming the centre of the projection and the parallels
are concentric circles.
• The meridians are straight lines radiating from pole having correct angular
distance between them.
• The meridians intersect the parallels at right angles.
• The parallels are unequally spaced. The distances between the parallels
increase rapidly toward the margin of the projection. This causes
exaggeration of the scale along the meridians.
• The scale along the parallels increases away from the centre of the
projection.
• The exaggeration and distortion of shapes increases away from the centre
of the projection. The exaggeration in the meridian scale is greater than
that in any other zenithal projection.
34. Properties of Bonne’s Projection
• Pole is represented as a point and parallels as concentric arcs of circles
• Scale along all the parallels is correct
• Central meridian is a straight line along which the scale is correct.
• Other meridians are curved and longer than corresponding meridians on
the globe. Scale along meridians increases away from the central meridian
• Central meridian intersects all parallels at right angle. Other meridians
intersect standard parallel at right angle but other parallels obliquely.
Shape is only preserved along central meridian and standard parallel
• The distance and scale between two parallels are correct. Area between
projected parallels is equal to the area between the same parallels on the
globe. Therefore, is an equal area projection
• Maps of European countries are shown in this projection. It is also used for
preparing topographical sheets of small countries of middle latitudes.
36. Properties of Polyconic Projection
• The parallels are arcs of circles with different centers
• Each parallel is a standard parallel i.e. each parallel is developed
from a different cone
• Equator is represented as a straight line and the pole as a point
• Parallels are equally spaced along central meridian but the distance
between them increases away from the central meridian.
• Scale is correct along every parallel.
• Central meridian intersects all parallels at right angle so the scale
along it, is correct. Other meridians are curved and longer than
corresponding meridians on the globe and so scale along meridians
increases away from the central meridian.
• It is used for preparing topographical sheets of small areas.
38. Properties of Sinusoidal Projection
• The central meridian is a straight line and all other meridians are
equally spaced sinusoidal curves.
• The parallels are straight lines that intersect centre meridian at right
angles.
• Shape and angles are correct along the central meridian and
equator
• The distortion of shape and angles increases away from the central
meridian and is high near the edges
• Equal area projection
• Used for world maps illustrating area characteristics. Used for
continental maps of South America, Africa, and occasionally other
land masses, where each has its own central meridian.
42. Properties of Mercator Projection
• Parallels and meridians are straight lines
• Meridians intersect parallels at right angle
• Distance between the meridians remains the same but distance between the
parallels increases towards the pole
• The length of equator on the projection is equal to the length of the equator on
the globe whereas other parallels are drawn longer than what they are on the
globe, therefore the scale along the equator is correct but is incorrect for other
parallels
• As scale varies from parallel to parallel and is exaggerated towards the pole, the
shapes of large sized countries are distorted more towards pole and less towards
equator. However, shapes of small countries are preserved
• The image of the poles are at infinity
• Commonly used for navigational purposes, ocean currents and wind direction are
shown on this projection
