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Essay on Maps!
Essay on Maps and Scales:
The earth is spherical. As such, it is represented by three dimensional model called globe. Even though, globe is very useful to maintain the true shape, area, direction, distances and locations, it cannot be made large enough to include all the details of surface features like— continents, oceans, mountains, deserts, roads, railways etc. Therefore, a two dimensional flat surface is constructed to represent the whole part of the earth and its surface features which is called Map.
Earth can be mapped through various ways like:
(i) Free hand sketches
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(ii) Actual survey with the help of some instruments
(iii) Using ground and aerial photograph
(iv) Satellite and rather charts
(v) High speed computers and
(vi) Global Positioning System (GPS).
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The number of information in a map depends on the following:
(a) Scale
(b) Projection
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(c) Conventional science and symbols
(d) Method of map making
(e) Requirement of the user and
(f) Skill of the cartographer.
Essay on Types of Map:
Based on the scale, purpose or content maps are broadly classified in the following manner:
Based on the Scale:
The maps may be called as large scale maps when they represent a small area of the earth on a large sheet of paper. The cadastral maps and topographical maps are large scale maps. Here, scale is normally 1:50,000.
A map is called small scale when it covers a large area on a small sheet of paper. They include wall maps, Atlas and thematic maps like soil map, climate map, weather map, natural vegetation map etc. The scale of small scale map is normally 1:1,00,000 or more.
All maps whether large scale or small scale differ in their purpose and content like physical, cultural and military uses.
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Essential Features of Map:
Normally the essential features of a map includes:
(i) Title—tells about the area and purpose
(ii) Scale—measures the distances
(iii) Map projection—surface created with the help of some techniques to construct network of parallels and meridian.
(iv) Key—tells about various signs used in the maps
(v) Direction—tells about the orientation
(vi) Conventional symbols—used to show various features
Scales:
Definition:
Scale is the ratio of distance between two points on a map and the corresponding distance on the actual surface of the earth.
Why necessary? A scale permits a portion of the earth’s surface to be represented on the map smaller than reality. From this, we can see that with smaller scale, larger areas can be represented on a sheet of paper but with lesser details. For example, 1 cm to 10 Kilometres. Similarly larger the scale, smaller will be the area with greater details. For example, 10 cms to 1 cm.
Representation:
There are three ways of representing scale on the map.
(a) Word Scale: like—one centimetre equal to 10 Kilometres.
(b) Representative Fraction (R.F.) Scale:
Like 1:25,000. This signifies that one unit on the map is equal to 25,000 units on the ground. The unit may be centimetre, or inch. Remember that R.F. is expressed by a fraction in which the numerator is always shown by unit.
(c) The line Scale like
Here, distance is represented along a line drawn along either at the top or at the bottom border of the map.
Conversion of Scales:
For convenience, sometimes one type of scale is converted into another type in the following manner.
Example 1:
Find R.F. when the scale in 4 cm. to 1 kilometre.
Remember, 1 km = 1,00,000 cm
... 4 cms represent = 1,00,000 cms
= 25,000 cms
Therefore, R.F. = 1 : 25,000 or 1/25,000.
Example 2:
The R.F. of a map is 1: 5,00,000. Convert it into a statement scale in metric system.
Here, 1 cm, represents 5,00,000 cms.
Remember, 1,00,000 cms = 1 km
.
= 5 kms.
... The statement scale is 1 cm to 5 kms.
Plain Scale:
A plain scale consists of primary and secondary divisions to measure larger and smaller units of measurement on a map.
Remember:
The length of a primary scale is to be kept between 10 cm to 15 cm for convenience.
The construction of a plain scale is explained with the help of a worked out example.
Example 3:
The R.F. of a map is 1:50,000. Draw a plain scale to read kilometres and metres.
Remember, 1,00,000 cms = 1 km
Here, 1 cm= 50,000 cms
= 0.5 kms
... 2 cms = 1 km
If we choose to make the scale 10 cm long
10 cms. will represent 0.5 x 10 = 5 kms.
Now, draw a line AB = 10 cms long in your paper (preferably at the middle). It will measure 5 kms. on the ground. If the line is marked at an interval of 1 cm, the line will be divided into 10 equal parts. Each one of the divisions is called primaries and measures 0.5 km or 500 metres.
Now, divide one of the primaries to the extreme left AC into (say) 5 equal divisions. Each of such divisions is called secondaries and will measure 100 metres or 0.1 kms.
Important:
The length of the line AB can have fractions like 10.56 cm, 12.73 cm, etc. But, the distance represented along this line should always have whole number like, 5,10,100,250 kms. etc.
ANOTHER EXAMPLE when AB has fractional length.
Example 4:
The R.F., of a map is 1 : 74,000. Construct a plain scale in metric system 10 read kms and metres.
Remember, 1,00,000 cm = 1 km
Here, 1 cm. = 74,000 cms
= 0.74 kms
If we choose to have a scale of 10 cm. long;
10 cms will represent 0.74 x 10 = 7.4 kms.
Now, 7.4 kms. are represented by 10 cms.
Step I: (To make primary divisions)
1. Draw a line AB = 10.8 cms to represent 8 kms.
When AB is divided into 8 equal parts, each one will measure 1 km.
2. Draw another line AC = (say) 8 cms at an angle between 200 to 250 with AB.
Remember, Length of AC should always have whole number.
3. Mark AC at an interval of 1 cm with the help of a scale or by compass.
4. Join CB and draw straight lines through the marked points on AC parallel to CB. These lines will divide AB into 8 equal parts and each one will measure 1 km. These are primary divisions.
5. Number the primary divisions form 0, 1, 2,………, 8 as shown in the figure.
Step II: (To make secondary divisions)
1. Along AB, at A draw a perpendicular, AD above AB and at 0 draw another perpendicular OE below AB.
2. If you are interested to measure in multiple of 200 metres, make out 5 divisions at selected intervals along the two perpendiculars.
3. Join A with the end point E of lower perpendicular and 0 with the end point D of upper perpendicular.
4. Join other marked out points consecutively as shown in the figure.
5. These lines will divide the primary division AO into 5 equal parts each measuring 200 metres.
This is the construction of a plain scale to measure kilometres and metres.
Remember:
Line AC to be drawn equal to the length you want to represent.
1. Perpendiculars are to be drawn one above and the other below AB in opposite directions.
2. Divisions are to be marked out according to the amount of smaller distance to be measured by each secondary unit.
Comparative Scale:
Comparative scales are special types of plain scale drawn side by side to measure distances in different unit of measurements. Method of construction is same as plain scale. Study the following example for clarification.
Example 5:
The R.F. of a map is 1 : 1,00,000. Draw comparative scales to show kilometres and miles.
For Kilometre Scale, 1 cm represents, 1,00,000 cms. or 1 km.
... (say) 12 cms represent 12 km.
Draw a line AB = 12 cms. to represent 12 kms. Divide AB into 12 equal parts and each one will represent 1 km. If one of the divisions near A is subdivided into 5 equal divisions each one will measure 200 metres,
For Mile Scale, 1 inch represents 1,00,000 inches
Remember, 63,360 inches =1 mile
Or (100000/63368) miles
or 1.57 miles That is, 1.57 miles are represented by 1 inch.
... 10 Miles are represented by (1 x 10)/1.57 = 6.35 inches
To draw the plain scale CD to represent miles and furlongs, follow the steps mentioned in example 4.
Now draw the two scales one above the other in such a way that the zero points coincide.
Important:
In comparative scale Zero markings of both the scales are to be coincided.
Time Scale:
The time scale is constructed for a moving body to give a time and space relationship. It is also a special type of plain scale.
Important:
In the scale two things are necessary:
(a) The scale of the map
(b) The rate of movement or speed.
The method of construction is same as plain scale.
Example 6:
Draw a time scale for a car moving at 30 kms. per hour on a map having R.F. 1 :10,00,000.
Remember, 1,00,000 cms = 1 km
Here, 1 cm represents 10,00,000 cms. or 10 kms.
... 12 cms represent = 10 x 12 kms.
= 120 kms.
Now, the car moves 30 kms in 1 hour.
... To cover 120 kms, the car needs = (120/30) = 4 Hours
Construction (Steps to be followed)
(i) Draw a straight line AB = 12 cms.
(ii) Divide it into 4 equal divisions. Each division will represent 1 hour as well as 30 kms.
(iii) Take one of the divisions near A and divide it into 3 equal sub-divisions. Each sub-division will represent 20 minutes as well as 10 kms.
Important:
1. The length of the scale is to be determined according to the given scale of map.
2. The primary and secondary divisions are to be made according to the rate of movement.
Diagonal Scale:
For greater accuracy of measurement even the secondary divisions of a plain scale are to be sub-divided into tertiary divisions. The scale which contains primary, secondary and tertiary divisions is called Diagonal scale. That is, with Diagonal scale measurements can be taken upto 2 places after decimal.
Remember, construction of primary and secondary divisions is same as plain scale.
Example 7:
Draw a diagonal scale to read upto two places after decimal of millimetre for a map with R.F. 1: 1,00,000.
Remember, 1,00,000 cm = 1 km.
Here, 1 cm represents 1,00,000 cms or 1 km.
10 cm represents 10,00,000 cms or 10 kms
Steps to be followed: (To make primary divisions)
1. Draw a Line AB = 10 cms.
2. Divide AB into 5 divisions at an interval of 2 centimetres. Each of the 5 divisions will measure 2 kms.
3. Mark them as 0, 2, 4, 6 and 8 along AB.
(To make secondary divisions)
4. Divide one of the primary divisions near A into 5 equal parts. They are called secondary. Each one of the 5 secondary divisions will measure 0.4 kms.
5. Mark them as 0.4, 0.8, 1.2, 1.6 and 2.0 as shown in the Figure.
(To make tertiary divisions)
6. Draw two perpendiculars at A and B.
7. Markout equal divisions according to your choice at the interval of say 0.5 centimetres on the two perpendiculars.
8. Draw straight lines through the marked points parallel to AB.
9. At the uppermost straight line, mark out the positions of the secondaries and number them as shown in the Figure.
10. Draw perpendiculars at 0, 2, 4 and 6 on AB also.
11. Draw diagonals joining 0.4 of the uppermost line to zero of the bottom line; 0.8 and 0.4, 1.2 and 0.8; 1.6 and 1.2 and 2.0 and 1.6.
12. Each intersection of the straight lines and the diagonals will measure .08 kms.
Remember, the interval to divide the perpendiculars at A and B can be taken according to your choice.
Enlargement and Reduction of Maps:
Many a times maps are required to be enlarged or reduced according to need. There are several methods for this. The square Method is one of the most simple one.
Important:
1. It is based on the principle of adjusting distances according to scales.
2. The size of the squares of the first network is to be selected according to own convenience.
3. The size of the squares of the corresponding network will depend on the first.
Steps to be followed:
(i) Draw four boundaries on the given map.
(ii) Determine the squares side length to be drawn over the map.
Remember, square should not be too large or too small.
(iii) Divide the four boundaries according to the chosen interval (length).
(iv) Fill the map with squares by joining the points.
(v) Find out the length of the side of the small squares to make the corresponding network for the second map with the help of the formula given below.
Remember, X will have same unit as that of the square drawn already over the given map.
(vi) Draw a network of squares according to size of X.
(vii) Draw map with freehand.
Example 8:
A map of one Block is drawn on a scale with R.F. 1: 1,00,000. It is to be enlarged on a scale with R.F. 1:50,000.
Let us consider the length of the sides of the squares on the given map as 1 cm (say).
Therefore, length of the sides of the squares in the enlarged map will be
= 2 cms.
Map Projection:
Map projection is a method by which the network of parallels of latitudes and meridians of longitudes is transferred from the spherical globe to a two dimensional plane. Before discussing about the method it is necessary to understand some basic definitions which are necessary for any map projection.
Meridians of Longitudes:
The meridians of longitudes are semi circles joining the north and south poles. They intersect equator at right angles. They are of equal length. The value of a longitude varies from 00 to 1800 east or west at 10 intervals. The meridian that passes through Greenwich (near London) is called Prime Meridian.
Parallels Latitude:
The latitude of a place on the earth surface is its anguler distance north or south of equator from the center of the earth. The lines joining places of same latitudes are called parallels of latitudes. Given below is the 45° south parallel of latitude.
Longitude and Time:
The earth rotates from west to east. Therefore, a place west of ours will have sunrise and mid day later than our place. The time which is fixed on the basis of the position of the mid day sun is called Local Time. The earth takes 24 hours to complete one full rotation or to cover 360 degrees of longitude. Therefore, 1 degree longitude will be covered in 4 minutes (360 degree divided by 24 hours or 24 x 60 = 1440 minutes). Large variations are found from one place to the other within a country.
Therefore, it is necessary to consider the local time of a particular meridian as the standard one for the country. Such meridian is called Standard Meridian. In India, the 82 degree 30 minute meridian which passes through Allahabad is considered as Standard Meridian for the whole country. The time according to this meridian is called Indian Standard Time (IST).
Similarly, the Local Time of Greenwich near London with 0 degree meridian is considered as Greenwich Mean Time (GMT) or International Standard Time (IST). Our time is 5 hours 30 minutes ahead of GMT. The time for a band of 15 degree meridians to the east and west of Greenwich is called Time Zones. Therefore, there are 24 Time Zones in the world.
Classification of map projection:
The map projections are classified on the basis of:
(a) Source of light
(b) Developable surface and
(c) Global properties
There are three types of projections based on source of light:
(a) Perspective projections—which are drawn by projecting the network of meridians and parallels on a developable surface keeping the source of light at the center, infinity and certain convenient location of the globe.
(b) Non perspective projections—in these projections, the parallels and meridians cannot be transferred with the help of a source of light.
(c) Mathematics of conventional projections—these projections are drawn by mathematical computation and formula.
The projections are again classified on the basis of the developable surfaces as:
(a) Zenithal Projections—here the plane is kept tangential to the globe at some specific points.
(b) Conical Projections—here the cone is made to touch the globe along certain parallel of latitude and the plane is made by cutting open the cone from the apex to base.
(c) Cylindrical Projection—here a cylinder is assumed to touch the equator and its axis consists of the axis of the globe. The cylinder is cut open from the base to the top along a line to make a plane.
Map Projection/Means:
Drawing the network of parallels and meridians systematically over a piece of plain paper.
Important:
1. The network is also called, a grid, a net or a mesh.
2. The network is drawn following suitable scale.
3. The parallels and meridians may be straight lines, curves or circles.
4. Certain areas on the network may be of same size and shape while others may be reduced or enlarged.
Choices and Uses:
Map projection is to be drawn with three elements in mind:
1. Preservation of:
(i) Shape
(ii) Area
(iii) Distance and direction.
Therefore, different types of map projections are drawn to fulfill different elements mentioned above.
Remember:
Three things are necessary to draw projections—a globe, a piece of paper in the form of surface like—plane, Conical or Cylindrical and a source of light.
Zenithal Projections:
Zenithal projections are obtained by projecting parallels and meridians on a plane surface.
When the plane surface is tangent at the pole it is called Polar Zenithal. The projection is called Gnomonic when the source of light is at the centre of the globe. It is called stereographic when the light is at the circumference of the globe opposite to the plane surface.
Important:
In zenithal projection, direction is correct in all sides from the centre of the map.
1. Polar Zenithal Gnomonic Projection:
As the name implies, the plane surface is tangent at the pole and the source of light is at the centre of the globe.
Example:
Draw graticles of a Polar Zenithal Gnomonic Projection at 15° intervals for northern hemisphere. The scale is given as 1 : 3,00,000,000.
Remember:
1. Radius of the earth = 635,000,000 cms.
2. Plane surface is tangent at the north pole.
3. Source of light is at the centre of the globe.
4. Intervals for meridians and parallels are 15°.
Steps to be followed for construction:
(i) A circle to represent the globe is to be drawn first.
For this, calculate radius (R) according to given scale of the map.
= 2.17 cms or 2.2 cms (Approx.)
(ii) Draw a circle with radius (= 2.2 cms) preferably at the upper right or left side of the paper and let NS represents north and south poles, .EQ-equator and 0 centre of the globe.
(iii) Divide NQ at 15° intervals to make the positions of the parallels and mark them from Q as f, g, h, i, and j.
(iv) Draw a tangent NM parallel to EQ to represent the plane surface.
(v) Join the markings of NQ with 0 and extend to meet NM at f’, g’, h’, i’, j’.
Construction of Network:
(a) For drawing parallels:
(vi) Take a point N at the middle of your page.
(vii) Draw concentric circles, taking N as the centre with radius Nf’, Ng’, Nh’, Ni’, and Nj’ to represent 15°, 30°, 45°, 60° and 75° north parallels.
Remember:
1. Here 90° N parallel will be a point.
2. Equator can’t be drawn.
(b) For drawing meridians:
(viii) Draw a straight line vertically through N and number it zero at the bottom and 180° at the top.
(ix) Markout the positions of different meridians to east and west from zero at 15° interval.
(x) Join each of them with N and number them as 15°,30°,45°, 60°,75°, 90° ………. upto 180° east and west.
Properties:
1. Parallels are concentric circles
2. Meridians are radiating straight lines
3. The lengths of the parallels and meridians increase from the centre of the map outwards. That is, areas towards the equator are exaggerated.
Uses:
1. Projection is suitable for polar regions upto about 60°.
Now, follow the steps and complete the drawing –
2. Polar Zenithal Stereographic Projection
In this projection, plane surface is at one pole and the source of light is at the other pole.
Example:
Draw graticles of a Polar Zenithal Stereographic Projection for northern hemisphere at 15° interval.
The scale of the map is given as 1: 200,000,000
Steps to be followed for construction:
(i) Follow the steps (i) to (iv) exactly the same way as given in Polar Zenithal Gnomonic Projection.
(ii) Join the markings of NQ with S and extend to meet NM at q’, f’, g’, h’, i’, and j’.
(iii) Take a point N at the middle of your page.
(iv) Draw concentric circles taking N as the centre with radius Nq’, Nf’, Ng’, Nh’, Ni’ and Nj’ to represent 0°, 15°, 30°, 45°, 60° and 75° parallels.
(v) Follow the steps (viii) to (x) given under Polar Zenithal Gnomonic Projection.
Remember:
In this projection all the parallels except 90° N (which is the centre of the map) can be drawn.
Properties:
Same as Gnomonic projection. In this projection shape is maintained correctly.
Uses:
Suitable for polar areas, Map of one complete hemisphere can be drawn. It is suitable for navigational charts for high latitudes.
Now, complete the drawing by following the steps mentioned.
3. Polar Zenithal Equidistant Projection:
As the name implies, the parallels of this projection are drawn in such a way that they are equidistant from each other. On the graticule, parallels are drawn at their true distances.
Example:
Draw the graticules of a Polar Zenithal Equidistant Projection of northern hemisphere at 15° interval.
The scale is given as 1: 200,000,000.
Remember:
This is a non-perspective projection. That is, source of light is not considered.
Steps to be followed for construction:
(i) Complete steps (i) and (ii) of Gnomonic projection.
(ii) Draw 15° angle (∠QOR) on OQ.
(iii) Take a point N at the middle of your page. It will be the north pole in the map.
(iv) Draw a vertical line through N and mark out 6 divisions upward at ap interval of arc length QR. Let they be represented by a, b, c, d, e, and f.
(v) Draw concentric circles taking Na, Nb, Nc, Nd, Ne and Nf as radii to represent 75°, 60°, 45°, 30°, 15° and 0° parallels.
(vi) Draw meridians as before.
Properties:
1. Here, parallels are concentric circles and meridians are radiating straight lines from the centre of the map.
2. Distances and directions are correct from the central point to any other points.
3. In this projection central area also gets exaggerated.
Uses:
Suitable for polar areas but a complete hemisphere can also to be represented.
However, the area gets much exaggerated away from the centre.
Now complete the drawing following the steps mentioned.
Conical Projections:
Conical Projections are obtained by projecting parallels and meridians on a conical surface. The parallel along with the cone touches the globe is called standard parallel. In this type of projection, scale is correct only along the standard parallel.
Simple Conical Projection (with one standard parallel):
As the name implies, there will be only one standard parallel and the scale along this parallel will be correct.
Example:
Draw the graticule on a Simple Conical Projection with one standard parallel for the area covered by 15° N to 75°N latitudes and by 15°E to 135°E longitude. The scale of the map is given as 1:150,000,000 and interval 15°.
Remember:
1. Radius of the earth = 635,000,000 cm.
2. Cone will touch the globe along a parallel at the middle of the extension which will be called standard parallel.
3. The central meridian should also be at the middle of the map.
Steps to be followed for construction:
(i) According to the given scale, calculate the radius of the reduced earth following the formula,
.
= 4.2 cms.
(ii) Find out the value of standard parallel from the extension 15°W to 75°N, which should be at the middle of the map.
From 15°N to 75°N at the interval of 15°N, there will be 5 parallels as 15°N, 30°N, 45°N, 60°N and 75°N. Therefore, value of the standard parallel will be 45°N.
(iii) Find out the value of the central meridian from the extension 15°E to 135°E which should also be at the middle of the map.
At the interval of 15°, there will be 9 meridians as 15°E, 30°E, 45°E, 60°E, 75°E, 90°E, 105°E, 120°E and 135°E. Therefore, 75°E will be the central meridian.
(iv) Draw a circle with 4.2 cm radius centering at 0 at the top of your page.
(v) Draw EOQ as equator and NOS as polar diameter.
(vi) Draw ∠QOL = 45° and draw a tangent at L in such a way that it meets SON (when extended) at M. Now, ML will be the radius to draw the Standard parallel.
(vii) Draw ∠EOA = 15°. Now, EA will be the distance between two parallels,
(viii) Again, draw a semi-circle at 0 with radius EA. The semi-circle will touch OL at X.
(ix) From X, draw a perpendicular XY on ON. Now, XY will be the distance between the meridians.
Properties:
1. The parallels are concentric circles, and equidistant.
2. The meridians are radiating straight lines from the apex of the cone.
3. Scale is correct along the standard parallel as well as meridians.
4. The pole is also represented by the arc of a circle. Hence, the areas away from the standard parallel are exaggerated.
Uses:
Projection is suitable for areas having smaller north-south but larger east-west extensions.
Now complete the drawing of the projection following the steps mentioned.
Cylindrical Projections:
Cylindrical Projections are obtained by projecting parallels and meridians on a cylindrical surface.
Important:
1. The cylinder touches the globe along the equator.
2. Light is placed at the centre of the globe.
3. It is a perspective projection.
Simple Cylindrical Projection:
In this projection, both the parallels and meridians are equidistant. They are drawn as straight lines, cutting one another at right angles. All the parallels are equal to the equator and all meridians are half of the equator. The scale along the equator and along all the meridians is correct. There is great distortion in shape of the area away from the equator.
Exercise:
Draw the graticules of a Simple Cylindrical Projection at 15° interval. The scale of the map is 1: 200,000,000.
Remember, Radius of the earth = 635,000,000 cm.
Length of the equator = 2πR.
Steps to be followed for construction:
(i) Calculate the radius of the reduced earth (R) according to the given scale.
= 3.18 cms.
(ii) Calculate the length of the equator (L).
L = 2πR
= 2 x 3.14 x 3.18 cms.
= 19.90 cms.
(iii) Calculate the distance (d) between the meridians along the equator at 15° interval.
= 0.821 cms.
Construction of the Network:
For drawing parallels:
(iv) Draw a circle NBSQ with centre 0 and having radius 3.18 cms. on the left hand side of your paper, (place the paper lengthwise). Here, BQ is the equator.
(v) Extend BQ to P in such a way that QP = 19.90 cms.
(vi) Divide QP into 24 divisions taking 0.82 cms interval.
(vii) Draw a straight line RT perpendicular to QP at the middle of QP.
(viii) Markout 6 divisions above and 6 divisions below QP along RT with same interval .82 cms.
(ix) Draw straight lines through these divisions parallel and equal to QP. These are your parallels.
(x) Number the 6 parallels above QP as 15°,30°, 45°, 60°, 75°, and 90° N and 6 parallels below as S and QP as 0°.
For drawing meridians:
(xi) Draw straight lines through the markings on QP parallel and equal to RT. These are the required meridians.
(xii) Number RT as 0° to the right as E and to the left as W at 15° interval.
Properties:
1. All the parallels and meridians are straight lines.
2. All the parallels are equal to the equator.
3. All the meridians are half of the equator.
4. Scale along the equator and meridians is correct but shape is not correct.
Uses:
As there is too-much exaggeration of the polar region, the projection is suitable for world map of equatorial region.
Important:
The pole which is a point on the globe is made equal to the length of the equator. So, there will be too much exaggeration way from the equator.
Now, complete the drawing of the projection following the steps mentioned.
Cylindrical Equal Area Projection:
In this projection, the area between two parallels is made equal to the corresponding area in the globe.
Important:
1. Rays of light are assumed to come from infinity.
2. Shape is highly distorted in the areas away from the equator towards the poles.
Exercise:
Construct the graticule of a Cylindrical Equal Area Projection at 15° interval. The scale is given as 1: 200,000,000.
Remember:
1. Radius of the earth = 635,000,000 cm.
2. Length of the equator = 2πR .
3. Interval of meridians along the equator
Steps to be followed for construction:
(i) Follow steps from (i) to (vii) of the Simple Cylindrical Projection.
(ii) Draw OA, OB, OC, OD, and OE starting from N and OF, OG, OH, OI and OJ starting from Q at 15° interval.
(iii) Draw straight lines through P, A, B, C, D, E, F, G, H, I, J and S parallel of QP. These will be the required parallels.
(iv) Follow steps (x) to (xii) as mentioned in the case of Simple Cylindrical Projection.
Properties:
1. All the parallels and meridians are straight lines.
2. Meridians are equidistant.
3. Spacing of the parallel decreases away from the equator.
4. All the parallels have same lengths to the equator.
Uses:
As shape is highly distorted in the polar region; the projection is useful to show distribution in the equatorial region.
Now, complete the drawing of the graticules following the steps mentioned.
Mercator’s projection:
Marcator’s Projection was invented by Geradus Mercator in 1569. This projection belongs to the cylindrical group of projections. It is a very famous projection ever devised. It is widely used for world map and is invaluable for navigation purposes both on the sea and in the air.
Properties of Mercator’s Projection:
1. Shape of Parallels:
The parallels of latitude are projected equal in length of the equator of the reduced earth.
2. The Parallel Scale:
The parallel scale along the equator is always true but it is exaggerated towards north and south. Polar regions are not shown in this projection.
3. Shape of Meridians:
The spacing of meridians is true to scale the equator.
4. Scale along Meridians:
The exaggeration of the scale along the parallels is accompanied by equal exaggeration of the scale along the meridians.
Example:
Construct a Macerator’s projection for the world map when R.F. is 1:320,000,000 and the latitude and longitude interval is 200.
Construction:
Steps to be followed:
1. Radius of the earth (R) = 637,000,000 cm
2. R.F. of the projection = 1: 320,000,000
3. Therefore, Radius of the Reduced Earth (r) can be calculated with the help of the following formula,
Radius of the reduced earth (r) = R.F./Radius of the earth (R)
= 1/ 320,000,000 ÷ 637,000,000
= 2 cm
4. Length of the equator on the globe = 2πr
= 2 x 22/7 x 2
= 12.57 cm
5. Now draw a line AB = 12.57 cm long to represent the equator.
6. Actually, the equator is a circle on the globe and is subtended by 360°. Since, the meridians are to be drawn at the interval of 20°, divide AB into 360 ÷ 20 or 18 equal parts.
7. Distance between two meridians on the equator will be:
Length of AB x interval/360 degree
= 12.57 x 20/360 = 0.698 cm or 0.7 cm
8. Draw perpendicular lines through the 18 markings each at a distance of 0.7 cm on the equator.
9. The distance of the parallels from the equator = Reduced value x r
10. To draw latitudes of 20, 40, 60 and 80 we will have to take the reduced values as 0.365, 0.763, 1.317 and 2.436 from the table.
11. Therefore distance of 20 degree parallel from the equator = 0.365 x 2 cm = 0.712 cm
Distance of 40 degree parallel from the equator = 0.763 x 2 cm = 1.526 cm
Distance of 60 degree parallel from the equator = 1.317 x 2 cm = 2.634 cm
Distance of 80 degree parallel from the equator = 2.436 x 2 cm = 4.872 cm
The 90 degree parallel cannot be drawn as the reduced value is infinity.
12. Now mark the points on both sides of the equator along any one of the perpendicular drawn on the equator.
13. Label all the parallels and meridians and the Mercators Projection is Ready.
Merits:
1. This projection is orthographic as each meridian intersects the parallel at right angles and the scale ratio remains constant throughout.
2. Shape is preserved in this projection.
3. It shows the correct directions, it is always valuable to the navigators and pilots.
4. This projection is useful to show tropical countries.
5. This is most appropriate projection to show drainage patterns, routes, ocean currents, wind systems etc. on world map.
Demerits:
1. In the high latitudes there is great exaggeration of scale along the parallels and meridians. It is because the scale along the parallels and meridians increases rapidly towards the poles.
2. The size of the countries near the poles is highly exaggerated as compared to its actual size.
3. Through this projection poles cannot be shown because of exaggeration of scale along the 900 parallel and the meridians touching them are infinite.