Map projection md. yousuf gazi

Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
GIS

❖ The basic purpose of a map projection is to transform the Earth’s globe into a
useable format for a specific application.
❖ A projection systematically transforms the geographic latitudes and longitudes
on the surface of the ellipsoid into locations on a plane.
❖ A map projection portrays a three-dimensional object, such as the Earth’s globe,
in a two-dimensional format.
❖ A two-dimensional plane cannot accurately represent large portions of the
rounded, curvilinear surface of the Earth.
❖ A map projection is a systematic rendering of locations from the curved Earth
surface onto a flat map
Map Projection
GIS

There are four important properties of the Earth model that can be tactically
preserved during a projection process:
▪ Area
▪ Shape
▪ Distance
▪ Angles
GIS

➢ There are three distinct types of projections that can be
utilized on the projected plane:
❑ Cylindric
❑ Conic
❑ Planar
➢ The projected plane inherits the display characteristics
associated with each projection type and forms what is
called a graticule.
➢ A graticule is basically a grid of meridians and parallels.
Types of Map Projections
GIS

❖ The cylindric projection type takes on the appearance
of a rectangular graph with an x (parallel) and a y
(meridian) axis.
❖ The globe’s longitudes (meridians) and latitudes
(parallels) are represented by equidistant, parallel
straight lines that intersect one another at right angles.
❖ The cylindric type projection is a strict grid
representation of the curvilinear surface that is true at
the equator and increases in distortion toward the
poles.
The Cylindric Type
GIS

❖ The Mercator projection is a good example of
the cylindric type.
❖ The graticule consists of equally spaced
meridians but unequally spaced parallels. As the
parallels get closer to the poles, the spacing
between each becomes wider.
❖ With this increase in width, there is an increase
in distortion. Therefore, the distortion increases
as the projection moves toward the poles.
Example of Cylindric Type
GIS

Most Accurate in the tropics from Cancer to Capricorn
Most Distortion at the North and South Poles
Used for: Locating Latitude and Longitude and Sea
Captains use it for navigation at sea.
Characteristics:
• All lines are at 90 degree angles
• Simplest to read
• Accurate direction
• Distorted size, distance, shape
GIS

❑ The conic projection type is fan shaped, characterized by
an upside down cone over the sphere.
❑ The meridians are represented by a system of equally
inclined concurrent straight lines, and the parallels are
represented by concentric circular arcs.
❑ The angle between any two meridians on the projection is
less than their true difference in longitude on the sphere.
❑ Conic classifications are at an exact scale along a
particular parallel, or standard parallel, between the
equator and a pole. Distortion increases away from the
standard parallel.
The Conic Type
GIS

❑ Current popular conic type projections are the Lambert
conformal conic, also known as the American polyconic,
used in state plane systems, and Albers equal area, used in
small-scale mapping.
Example of Conic Type
GIS

❑ The planar projection type is an azimuthal orientation of a projected
surface, which means that it pertains to the angle (usually in degrees)
of an object around the horizon that is measured from north to east.
❑ The planar type protects the integrity of azimuths, bearings, and
directions from a central point to other more remote points in the
plane. Therefore, planar projections are true only at their center point.
❑ The planar graticule represents meridians as straight lines that incline
toward each other at their true longitudinal difference.
❑ Parallels are represented by a system of concentric circles with their
common center at the point of converging meridians or pole. The
distortions in the planar type tend to be most prevalent along the edges
of the projected plane surface.
Planar Type
GIS

The Aspect of Projection
Projection aspect is the relative orientation of the projected
plane and the ellipsoid of revolution with respect to the
location of an observer.
Bringing this projection tool into perspective, there are four
predominant types of projection aspects:
Normal, Transverse, Oblique, and Polar.
Normal aspect Transverse aspect
Oblique aspect Polar aspect
GIS

The normal aspect is based upon a standard line along which
distortion is minimized. The farther you move away from the
standard line, the more the distortion. If this standard line is
coincident with the equator, or central parallel, its aspect is
considered to be equatorial.
Normal
GIS

In the oblique aspect, the axis of the Earth and the axis of
the projection are oriented in an arbitrary manner. The
oblique aspect is uniquely suited to be used for geographic
areas that are centered along lines that are neither meridians
nor parallels but are assumed to be “great circles” passing
through the region.
Oblique
GIS

An aspect is said to be transverse when a standard line
(normal) aspect is rotated 90 degrees. This transverse aspect
projection minimizes distortion along meridians and can
have azimuthal or equatorial alignment.
Transverse
GIS

❖ The polar aspect centers on a single point, either the north
pole or the south pole.
❖ Meridians are subsequently depicted as straight lines
radiating from this pole outward toward the equator.
❖ Angles between these meridians are always true in
relation to the longitude distance on the Earth’s globe.
❖ Latitudes (parallels) are equally spaced concentric circles
radiating from this same source pole.
❖ Polar aspect projections retain symmetry about any
meridian and distort between them.
Polar
GIS

❑ Projected surfaces can exhibit the properties of several
classifications simultaneously, though any surface will
potentially distort shapes, areas, angles, or distances at
some level. Since all distortions can be measured or
estimated, the selection of an adequate projection requires
specific knowledge of the application.
❑ As a result, the three types of projections (cylindric, conic,
and planar) can be combined with one or more of the
projection classifications to control the appearance and
distortion for any particular application.
❑ For example, a planar equal-area projection preserves
both angles and areas. The region of interest is accurately
represented in size while angles to other locations are also
preserved. The distances between the area of interest and
other locations are absorbed by the distortion.
.
There are four primary projection classifications:
1. Equidistant;
2. Azimuthal;
3. Equal area;
4. Conformal.
Classification of Map Projections
GIS

❑ A projection is considered equidistant when scale is true
along at least one line (a focal line) or from one or two
points (focal points) to all other points on the projected
surface. The focal points are usually at the projection
center or some other approximately central location on
the surface.
❑ Although no projection can provide a developable surface
with a perfectly uniform scale, equidistant projections
retain a true scale along these explicit focal features (focal
lines and points).
❑ Consequently, if these focal features are properly
developed, the entire projection surface will benefit from
their true scale.
Equidistant
GIS

❑ In an azimuthal projection, all points in relation to a
central point (such as a pole) are not deformed during the
projection process from globe to plane. The central point
occurs at the intersection of the tangential plane to the
ellipsoid of revolution, or, simply, where the projection
plane and the projected object meet.
❑ Azimuthal projections preserve the angular relationship
of all features in a plane to the central point.
❑ This central point has zero distortion because it is the only
point that is being truly represented in the projection.
Consequently, distortion gradually increases as distance
from this central point increases.
Azimuthal
GIS

❑ The classification is considered equal area when the relative
sizes of all features on a globe are maintained during the
projection process.
❑ An equal-area projection vigilantly retains area properties
of the spheroid on the plane surface through the use of
compensatory scale factors.
❑ This means that if area is to be preserved but scale cannot
be, then any given feature on a globe (such as a state)
requires a scale factor greater than 1.0 in one direction
and less than 1.0 in the other direction. Both scale factors
compensate for one another and, in doing so, retain the
area characteristic.
GIS

❑ Unlike equal-area projections, conformal projections have
equal scale factors in all directions at any one point on the
projection surface.
❑ Instead of preserving area or size, conformal projections
preserve shape. For this reason they are also referred to as
orthomorphic projections.
❑ A conformal surface is also defined as a plane on which
all angles at infinitely small locations are correctly
depicted.
❑ This projection classification increasingly distorts areas
away from the point or lines of true scale (a scale factor of
1.0) on the plane.
Conformal
GIS

Methods for Distortion Management
Redistribution of the Scale Factor
❑ A proven method of manipulating the effects of and
controlling the location of distortion is to modify or
redistribute the scale factor.
Changing Projection Aspect
❑ A change in the projection aspect is the most obvious and
fundamental method to minimize unwanted distortion.
Simply put, it is a change in the location of the
projection’s center point.
❑ When a projection aspect is changed, the distortion
pattern in the projected map space is modified whereby
areas of least distortion are relocated.
GIS

The Tissot Indicatrix
❑ In 1881, cartographer Nicolas Auguste Tissot published
his groundbreaking approach to distortion analysis, now
known as the Tissot indicatrix.
❑ The Tissot indicatrix is a helpful tool for visually
modeling distortion and for graphically analyzing the
distortion properties in a projected surface.
❑ Tissot’s approach to distortion analysis was clearly the
most innovative in his day and still remains an effective
method of interpreting a projection.
❑ It has two primary elements: the projected graticule and
geometric deformation indicators. Simply stated, the
indicatrix depicts the projected graticule as a distortion
graph and shows distortion as circles or ellipses at the
specific intersections in the plane
GIS

Map projection md. yousuf gazi

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Map projection md. yousuf gazi

Similar to Map projection md. yousuf gazi (20)

More from Md. Yousuf Gazi

More from Md. Yousuf Gazi (20)

Recently uploaded

Recently uploaded (20)

Map projection md. yousuf gazi