Fundamentals of map.pptx

7/28/2019 Fundamentals of map.pptx

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Fundamentals of Maps

DR. Mukta Girdhar


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What is a Map

Map is usually a two dimensional

representation (eg a flat piece of paper) of a

three dimensional object (eg the Earth)

occasionally it may be a three dimensional

object (eg a globe)

Maps are drawn to a scale

Maps generally have a reference system


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Five steps fro producing Maps


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Reference System:- Latitude &

Longitude, Grid
http://www.icsm.gov.au/mapping/coordinates.html


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Latitude

The first convention to bedeveloped was latitude. This isbased on long termastronomical observations

about how the sun is perceivedto move across the surface ofthe Earth.

These observations alsodeveloped the conventions that

the sun: rises in the east and sets in the

west


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line around the centre of theEarth would be called theEquator. This would benumbered as zero degrees (0)of latitude. From the Equator aseries of parallel lines wererecognised with the mostnorthern and southern pointsbeing called the North Poleand South Pole. These would

be numbered as 90 degreesNorth and South respectively(90N and 90S).


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Longitude Series of radiating lines which

run vertically around theEarth. They connected at bothends ie at the North Pole andthe South Pole. As a result ofthis, a series of slices muchlike slices of an orange arecreated. These are pointed attheir ends and broadest in themiddle.

It was agreed that a primaryline of longitude should be

identified and that this shouldbe zero degrees (0) oflongitude.


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Add Two Together


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Datum

How to transfer co-ordinate system on to the

surface of the earth.
http://www.icsm.gov.au/mapping/datums1.html


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Measurement system

Measurement system which is used calculate

the coordinates of points on the surface of

the Earth.
http://www.icsm.gov.au/mapping/surveying.html


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Projection

which allows the coordinates which have been

calculated using a measuring system, to be

displayed on a flat piece of paper.
http://www.icsm.gov.au/mapping/about_projections.html


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Different Earth Image


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Distortions

The direction between a feature and

surrounding features

The distance between a feature and

surrounding features

The shape of any feature

The size of any feature


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Block of 1x1


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Distortion


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http://www.icsm.gov.au/mapping/images/world_map-mercator.gif


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Datum

A datum is a system

which allows the

location of latitudes

and longitudes (and

heights) to be

identified onto the

surface of the Earth


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About the Geometry of Datums

In order to calculate where latitudes

and longitudes occur on the surface of

the Earth a number of fundamentalgeometric concepts and practices

need to be applied.


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The Earth as a Sphere

In this calculation theEarth is viewed as beingan evenly round

ball. This is called aSphere.

From an imaginary centreof the Earth, calculations

are made from the centreof the Earth to thesurface of the Earth.


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The Earth as an Ellipsoid (or Spheroid)

However, the Earth isnot evenly round - it isin fact wider around

the Equator than it isbetween the Northand South Poles.

This is called anEllipsoid (or aSpheroid).


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The Earths True Shape - Its Terrain

Earth isnt just ocean(Mean Sea Level). Much ofthe land masses are wellabove the sea level (eg

Mount Everest is over8,000 metres above MeanSea Level), while in theocean it is well below sea

level (eg the MarianaTrench is over 10,000metres below Mean SeaLevel.


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The Earth as a Geoid

The Earth in reality is a

very misshapen

object. This is called a

Geoid.

The Earths Geoid is

regarded as being equal

to Mean Sea Level.


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Relationship Between Four


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Geo Centric Datum


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Projection

A projection is aprocess which uses thelatitude and longitude

which has already beendrawn on the surfaceof the Earth using adatum, to then be

drawn onto a flatpiece of paper- calleda map.


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Projection

Basic Type: depends on the characteristic that

is preserved

Basic Technique: depends on the method

used to project features onto a flat surface


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Basic Projection Type

Equal-Areacorrectly shows the size of a feature

Conformalcorrectly shows the shape of features (A map can not be both equal-areaor conformal it can only be one; or the other; or neither.)

Equidistantcorrectly shows the distance between two features

True Directioncorrectly shows the direction between two features


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Basic Projection Techniques

azimuthal the imaginary piece of paper is flatthis is usually used over Polar areas

conical the imaginary piece of paper is rolled into acone this is usually used in mid-latitude areas(approximately 20 60 North and South)

cylindrical the imaginary piece of paper is rolledinto a cylinder this is usually used over Equatorialareas or for World Maps


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Azimuthal

the imaginary piece of paper is flatthis is usually used over Polar areas

These projections:

have distortions increasing away from the central point

have very small distortions near the centre point (thetouch point of the paper)

compass direction is only correct from the centre point

to another feature not between other features are not usually used near the Equator, because other

projections better represent the features in this area.
http://www.icsm.gov.au/mapping/coordinates.htmlhttp://www.icsm.gov.au/mapping/coordinates.html


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Azimuthal


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Circles are longitude


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Conical Projections


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These projections:

are fan shaped when used to map large areas

have distortions increasing away from the centralcircular line (the touch point of the paper)

have very small distortions along the centralcircular line (the touch point of the paper)

shapes are shown correctly, but size is distorted

usually have lines of longitude fanning out fromeach other and have lines of latitude as equallyspaced open concentric circles


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2-D Dimension


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Cylindrical / Mercator Projection


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These projections usually:

are rectangular or oval shaped but this

projection technique is very variable in its shape

have lines of longitude and latitude at right-angles to each other

have distortions increasing towards away fromthe central circular line (the touch point of thepaper)

have very small distortions along the central

circular line (the touch point of the paper) show shapes correctly, but size is distorted.


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Psudo Cylindrical or Robinson

Projection


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Universal Transverse Mercator System

(UTM)

In 1947 the North Atlantic Treaty Organisation (NATO)developed the Universal Transverse Mercatorcoordinate system (generally simply called UTM)

Regular grid system which covered the entire Surface

of the Earth. For low to mid-latitudes (0 to 80 Northand South) the IMW established a grid system that was6 of longitude wide and 4 of latitude high.

locations, shapes and sizes and directions between all

features are very accurate. Directions are not perfect.

A i l b f h M i


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A particular subset of the transverse Mercator isthe Universal Transverse Mercator (UTM) whichwas adopted originally by the US Army for large-

scale military maps. In the UTM system, the globeis divided into 60 zones between 84 S and 84 N,most of which are 6 wide. Each UTM zone has itsown central meridian and spans 3 west and 3

east from the center of the zone. Note that theposition of the cylinder developable surface ispositioned at a different place around the globefor each zone. X- and Y-coordinates are in meters

by convention.


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For zones in the northernhemisphere, the X-origin is aplace 500,000 m west of thecentral meridian, and the Y-originis the Equator. The false easting is

used to eliminate negativecoordinates.

For zones in the southernhemisphere, the X origin is also

500,000 m west of the centralmeridian, but the Y-origin is theSouth Pole.

Fundamentals of map.pptx

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