MAP PROJECTION IN GIS.pptx

Samirsinh P. Parmar
Dept. of Civil Engineering
Dharmsinh Desai University, Nadiad
Mail: spp.cl@ddu.ac.in, samirddu@gmail.com

2
Map Projections in GIS, Samirsinh Parmar, DoCL, DDU, Nadiad.

Projection
Transformation of Three Dimensional Space onto a
two dimensional map
A systematic arrangement of intersecting lines on a
plane that represent and have a one to one
correspondence to the meridians and parallels on
the datum surface
3

Developable Surfaces
4

Classification
A) Based on Extrinsic property
 Nature:
 Plane, Cone, Cylinder
 Coincidence:
 Tangent, Secant, Polysuperficial
 Position:
 Normal, Transverse, Oblique
5

Azimuthal Projections
6

Cylindrical Projections
7
Tangent
Oblique
Transverse
Secant

Conic Projections
8

Classification contd.
B) Based on Intrinsic Property
 Property of Projection:
 Equidistant
 Conformal or Orthomorphic
 Equivalent or Equal area
 Generation:
 Geometric, Semi Geometric, Mathematical
9

Cylindrical Map Projections
 Cylindrical map projections are made by projecting from the globe onto the
surface of an enclosing cylinder, and then unwrapping the cylinder to make a
flat surface
 Mercator
 Transverse Mercator
 Cassini-Soldner
10

Mercator Projection
 Cylindrical, Conformal
 Meridians are equally spaced straight lines
 Parallels are unequally spaced straight lines
 Scale is true along the equator
 Great distortion of area in polar region
 Used for navigation
 Limitations
11

12
REGULAR CYLINDRICAL PROJECTION:
THE MERCATOR

13

Transverse Mercator Projection
 Cylindrical (Transverse)
 Conformal
 Central meridian and equator are straight lines
 Other meridians and parallels are complex curves
 For areas with larger north-south extent than east-west extent
14

15
TRANSVERSE CYLINDRICAL PROJECTION:
THE TRANSVERSE MERCATOR

Cassini- Soldener Projection
Cylindrical, Tangent, Transverse
Equidistant
Cylinder is tangent along the meridian centrally located
Scale deteriorates away from central meridian
Normally used in 70 km belt from the central meridian,
as linear distortion factor at 70 km is 1.00006
Used for old cadastral surveys in India.
16

17
CASSINI-SOLDENER PROJECTION

Conic Projections
18
 For a conic projection, the
projection surface is cone shaped
 Locations are projected onto the
surface of the cone which is then
unwrapped and laid flat

Lambert Conformal Conic Projection
 Conical, Conformal
 Parallels are concentric arcs
 Meridians are straight lines cutting parallels at right angles.
 Scale is true along two standard parallels, normally, or along
just one.
 It projects a great circle as a straight line – much better than
Mercator
 Used for maps of countries and regions with predominant
east west expanse
 Used for plane coordinate system (SPCS) in USA
19

20
LCC PROJECTION

21
LCC PROJECTION

Polyconic Projection
In this projection all parallels are projected without
any distortion
Scale is exact along each parallel and central
meridian.
Parallels are arcs of circles but are not concentric.
It is neither conformal nor equal area.
22

Polyconic Projection contd.
Central meridian and equator are straight lines;
all other meridians are curves.
Central Meridian cuts all parallels at 90 degrees
Free of distortion only along the central
meridian.
It has rolling fit with adjacent sheets in EW
direction.
Used in India for all topographical mapping on
1:250,000 and larger scales.
23

24
Three partial equidistant conic maps, each based on a different standard
parallel, therefore wrapped on a different tangent cone (shown on the right
with a quarter removed plus tangency parallels). When the number of cones
increases to infinity, each strip infinitesimally narrow, the result is a
continuous polyconic projection

25
POLYCONIC PROJECTION
CENTRAL MERIDIAN: 100° W

Azimuthal Projections
 For an azimuthal, or planar projection, projected forward onto
a flat plane.
 The normal aspect for these projections is the North or South
Pole. locations are
26

Universal Polar Stereographic (UPS)
 Defined above 84 degrees north latitude and 80 degree south
 Conformal
 Meridians are straight lines
 Parallels are circles
 Scale increases from center point
 Used in conformal mapping of polar regions
27

28

Grids
 Rectangular grids have been developed for the use of Surveyors.
 Each point can be designated merely by its ( x , y ) co-ordinates.
 Grid systems are normally divided into zones so that distortion and
variation of scale within any one zone are kept small.
 The UTM grid
 State Plane Coordinate System (SPCS)
29

False Northing and False Easting
 Calculating coordinates is easier if negative number aren’t involved.
 Indian Grid and Universal transverse Mercator coordinates
 Expressed in coordinate units, not degrees.
30

31
SPECIFYING AN ORIGIN SHIFT:
THE FALSE EASTING AND FALSE NORTHING
Central Meridian
Natural Origin
Central Parallel
Coordinate System
Origin
False Easting
False
Northing

Universal Transverse Mercator (UTM)
 Particular case of Transverse Mercator Projection.
The earth between latitudes 84 N and 80 S, is divided
into 60, 6 wide strips;
Latitude origin – the Equator
Assumed (false) northing (y) at Equator
0 m for northern hemisphere
10,000,000 m for southern hemisphere
Assumed (false) easting (x) at Central Meridian
500,000 m
Scale factor at the central meridian : 0.9996
32

33
Figure

34

Projection Parameters
To define the coordinate system completely, it is not
sufficient simply to name the kind of projection used,
it is also necessary to specify the projection
parameters.
The set of parameters required depends on the kind of
projection.
The central meridian of the projection for cylindrical,
where it touches the ellipsoid surface.
35

Projection Parameterscontd.
 The standard parallel(s) for conic projections.
 The false easting and false northing
 The units
 Reference ellipsoid
36

Choosing a map Projection
The choice of map projection is made to give the most
accurate possible representation of the geographic
information, given that some distortion is inevitable.
The choice depends on:
The location
Shape
Size of the region to be mapped
The theme or purpose of the map
37

38
SHAPE OF AREA

Some Related Terms
 Coordinate System
 Reference Ellipsoids
 Everest Ellipsoid
 GRS 80
 WGS 84
39

Implications for GIS
Knowing the datum and reference ellipsoid
information is very important.
For converting the maps of one system to another
system.
When incorporating maps or GPS field data into a
GIS
40

Coordinate System
Need to describe the location, i.e. referencing
network by which positions are measured and
computed.
Relative location (with respect to some other place).
E.g. Street address.
• Absolute location (with respect to the Earth as a
whole).
E.g. Geographic coordinates
41

Objects in Real World
(Earth)
Geographic Coordinates
( ø , λ )
Represented on Paper
or Screen
(Map)
Planar Coordinates
( x , y )
42

REFERENCE ELLIPSOID
 All the measurements are done on the surface of the Earth.
Various computations are required to determine the
coordinates, distances, area etc.
 The surface of the earth is irregular and therefore unsuitable
for such computations. We need a smooth mathematical
surface for these computations.
 The best mathematical figure that can represent the earth is
an ellipsoid. Ellipsoid is used as reference surface.
43

TYPES OF ELLIPSOIDS
1. Best-Fit Ellipsoid/Local Ellipsoid: based on the measurements
within a region, so it best fits that region only. The centre of
such reference ellipsoid does not coincide with the centre of
gravity of the Earth.
Example : Everest Ellipsoid
2. Geocentric Ellipsoid: The centre of geocentric ellipsoid
coincides with the centre of the Earth. This type of the
ellipsoid can be used worldwide.
Example : WGS 84 ellipsoid
44

45
Best Fit and Geocentric Ellipsoids
Centre of Best Fit
Ellipsoid
Centre of Geocentric Ellipsoid
Best Fit
Ellipsoid
Geocentric Ellipsoid
Earth Surface
Best Fit
Ellipsoid

DATUM
Datum is a model that describes the position,
direction, and scale relationships of a reference
surface to positions on the surface of Earth
Indian Datum
WGS 84
ITRF
46

Scale
Only on a globe is a scale constant. It is impossible
to have a constant scale in different areas of a map
(but we can get close)
Map has fixed scale but GIS is scale-less, i.e. data
may be enlarged or reduced to any size.
However, if we go too far from the scale at which
map was made before it was captured into the GIS,
problems of scale appear.
47

Map Distance
Scale = -----------------------------
Ground Distance
 Representative fraction (RF) is the ratio of distances on the map to the
same distance on the ground. E.g., 1 : 1,000,000 or 1/1,000,000
 Statement (verbal) scale expresses the ratio in words. for 1 : 1,000,000 :
“One millimeter to one kilometer”
 Bar scale is a linear graphical scale drawn on the map
48

Scale in Map Projections
49

Conclusions
 We need to project geospatial data for any analysis
 Makes it possible to use data from different sources
 Several Projections to choose from
 Projections inevitably distorts at least one property
 Can choose suitable Map Projection
 Can control scale error
50

51

MAP PROJECTION IN GIS.pptx

More Related Content

What's hot

Similar to MAP PROJECTION IN GIS.pptx

More from Dharmsinh Desai of University

Recently uploaded

MAP PROJECTION IN GIS.pptx