Coordinate System and Projection System

Question 1

coordinate systems

Answer 1

a system which uses one or more numbers to uniquely determine the position of a point or other element within a space

Question 2

properties that define a coordinate system

Answer 2

definition of axis: number, name, order/sequence

definition of measurements: unit, direction (positive/negative)

Question 3

3 kinds of coordinate systems

Answer 3

observer based - azimuth and altitude
earth based - latitude and longitude
celestial - declination and right ascension

Question 4

earths rotation

Answer 4

counter clockwise

• provides an axis connecting north and south poles
• provides the basis for a system to determine location
• geographic coordinate systems or geographic grid

Question 5

one rotation takes

Answer 5

a solar day (24hrs)

Question 6

parallels define

Answer 6

degrees latitude relative to the equator

Question 7

meridians define

Answer 7

define degrees longitude relative to prime meridian

Question 8

network of lines

Answer 8

• east-west (parallels)

- north-south (meridians)

Question 9

construction of parallels

Answer 9

Starting point is the axis of rotation
Equatorial plane
Imaginary plane through center of the earth
Perpendicular to the axis of rotation
Latitude
The angular distance towards north or south of the equator from the equatorial plane
00 at the equator and +900 at the North pole and -900 at the South pole

Question 10

concept of small circles

Answer 10

circles produced by a plane passing through a sphere anywhere except its center are referred to as small circles
all parallels except the equator are small circles

Question 11

concept of great circles

Answer 11

if a sphere is divided exactly in half by a plane passing through its centre, the intersection of the plane with the sphere represents the largest circle that can be drawn on the sphere

Question 12

properties of great circles

Answer 12

1. great circles are the largest circles that can be drawn on a spherical surface
2. an infinite number of great circles can be drawn on a sphere
3. Only one great circle can be drawn to pass through two points on the surface of a sphere – unless
   the two points are the ends of the same diameter
4. An arc of a great circle is the shortest distance of two points on the surface of a spheroid

Question 13

Construction of meridians

Answer 13

Construction of meridians
Meridians are halves of great circles
Extend from north pole to south pole
No convenient place to start
Arbitrary starting point 
Meridian passing through Greenwich, England is the 0 meridian or prime meridian
Longitude
Angle between prime meridian plane and the meridian plane from the point of interest.

Question 14

longitude is expressed in

Answer 14

degrees, minutes and seconds 
Indicate east-west position
West of prime meridian: W
East of prime meridian: E
Prime meridian 0o
Meridians are between 0o -180o
Western hemisphere
Eastern hemisphere

Question 15

shortest distance between two points always

Answer 15

lies on a great circle

Question 16

distance from the lat/long

Answer 16

Along the meridian (north-south) 
	= Earth’s Circumference/360	= 111 Km (approx.)
Along the parallel (east-west)
	= depends of the latitude
	= cos(latitude in degree) * (111)

Question 17

what is projection

Answer 17

is a method of transferring features of the spherical Earth to a flat surface

Question 18

map projections define

Answer 18

the spatial relationship between locations on earth and their relative locations on a flat map

Question 19

methods of projection

Answer 19

A method of projection provides an orderly system of parallels and meridian that is used to model the relative location of earth surface features on a two dimensional media.

i. e., mathematica system - Robinson projection, mollweide projection
i. e., geometric - lambert conformal conic, north pole azimuthal equidistan projection
i. e., Mercator projecting

Question 20

conceptual model of deriving map projections

Answer 20

1. a transparent globe with geographical grid and may be continents are drown on it
2. a light source placed inner side (center…) of the globe
3. a paper placed on the surface of the globe in flat or conical or cylindrical shape

Question 21

why different types in conic, planar and cylindrical projection systems

Answer 21

Mapmakers and mathematicians have devised almost limitless ways to project the image of the globe onto papers to serve various purposes 
For Navigation (Mercator)
To show different parts of the world more accurately
To show world map more accurately
To show distribution patterns (Robinson)
For Administration………
ArcGIS supports 66 different types of map projections

Question 22

Which projection is the best?

Answer 22

No matter how we model our Earth, as spheroid, or on a two-dimensional flat surface, - each a less accurate than the preceding shape.
Every projection has its own set of advantages and disadvantages.
There is no “the best” projection.

Question 23

Spatial properties of earth surface features

Answer 23

No single projection can preserve, simultaneously, all of the main spatial properties –
angle, direction, distance, shape, area
On a map, the direction is correct means the bearing between two points is correct on anywhere on the map
If a projection preserves shape and area on the map, an area is uniformly proportional to the real world that they represent.

Question 24

Conformal Projection

Answer 24

– preserves the correct shapes of small areas.

Question 25

Equal Area Projection

Answer 25

- quadrilaterals formed by meridians and parallels have an area on the map proportional to their area on the globe.

Question 26

Equidistant Projection

Answer 26

- distance from a single location to all other locations are preserved.

Question 27

Azimuthal Projection

Answer 27

– directions from a single location to all other locations are preserved

Question 28

Compromise Projection

Answer 28

attempt to balance between the above characteristics, and is often used in thematic mapping.

Question 29

popular map projections

Answer 29

Mercator (Cylindrical) Lambert conical conformal (Conical) Transvers Mercator (transvers Cylindrical)

Question 30

Some projections cannot be expressed geometrically, have only mathematical descriptions

Answer 30

Goodes Robinson Molleweide Eckert

Question 31

Gerardus Mercator Projection

Answer 31

a cylindrical projection with rectangulargrid Distance between parallel increase with latitude Polar cut-of at 800 N and 800 S High distortion of shape and area toward pole,e.g.: Greenland shows same size as Africa Scale on 600 latitude is 2 times (on 800, it 6X)of that on the equator Impotent properties preserves direction (bearing), which makes it Indispensable for navigation Other uses  to show linier features like wind flow line, ocean currents, global temperature and pressure patterns

Question 32

Polar Projection

Answer 32

Can be centred on either the North or South Pole Meridians are straight lines radiating outward from the pole Parallels are nested circles centred on the pole Parallels with the meridians intersect at right angles The space between the parallels increases outward from the centre shows the true shapes of small areas,such as islands Scale increases away from the centre shapes look disproportionately larger toward the edge of the map

Question 33

Goodes Projection

Answer 33

Uses two sets of mathematical curves to form its meridians Between the 40th parallels, it uses sine curves Beyond the 40th parallel, towards the poles, it uses ellipses Ellipses converge to meet at the pole, so the entire globe can be shown Commonly used to show regional distributions of geographical features such as socials and vegetation. Shows area in correct proportion. It distorts the shapes of areas, particularly in high latitudes.

Question 34

Why is projection necessary?

Answer 34

Data often comes in geographic, or spherical coordinates (latitude and longitude) and cant be used for area calculations in most GIS software applications

Question 35

Angular Parameters

Answer 35

Central meridian or longitude of origin Latitude of origin or central parallel Longitude of center Latitude of center Standard Parallel

Question 36

Linear Parameters

Answer 36

False easting False northing Scale factor

Question 37

How to choose projections

Answer 37

Follow the lead of people who make maps of the area you are interested in. For a map of Canada Lambert Conical Conformal projection is commonly used. State plane is a common projection for all states in the USA. UTM is commonly used and is a good choice hen the east-west width of area does not exceed degrees.

Question 38

Commonly used Datum Systems in Canada

Answer 38

WGS84 (World Geodetic System of 1984) - geodetic coordinate reference system (datum) developed and used by GPS. No physical monuments. NAD83 (North American Datum of 1983) - developed based on GRS 1980. The ellipsoid defined through the use of satellites. Tied to the North American tectonic plate, meaning over time it diverges from WGS84. NAD27 (North American Datum of 1927)-developed based on the Clarke Ellipsoid of 1866. Discontinued from use but there are still use. It coordinate difference from NAD83 depends on the location ~20 m around Thunder Bay.

Question 39

Transverse Mercator

Answer 39

Whole Earth can be shown, but all distances, direction, shapes, and areas are reasonably accurate within 15 degrees of the central meridian. Distances are true only along the central meridian selected by the mapmaker or else along two lines parallel to it This is an ellipsoid cylindrical projection that divides the world into numbered zones in longitude. 20 latitudinal zones from 80 degrees south to 84 degrees north denoted by letters C to X, omitting the letters I & O. Each zone is 8 ^^0 south-north (except the "X" is 12 degrees) Areas are referenced by quoting the longitudinal zone number, followed by the latitudinal zone letter.

Question 40

UTM Coordinates - Northern Hemisphere

Answer 40

UTM projection use easting and northing in metres for coordinates. The central meridian's coordinate is always 500,000 The Equators coordinate is designated 0 for quadrangles in the Northern Hemisphere

Question 41

UTM Coordinates - Southern Hemisphere

Answer 41

The central meridian's coordinate is always 500,000 The equator's coordinate is designated 10,000,000 for quadrangles in the southern hemisphere

Question 42

UTM Accuracy

Answer 42

Each zone is separately projected using the ellipsoidal form of the transverse Mercator projection with a secant case: - scale of the central meridian is reduced by 0.04% so two lines about 1 degree 37" east and west of it have true scale The UTM grid was designed for large-scale topographic mapping in separate sheet, not for world or regional maps

Question 43

Earth Orbital Revolution

Answer 43

An elliptical path around the Sun Earth-Sun distance varies between aphelion and perihelion points 23.5 degrees with the ecliptic plane

Question 44

Celestial Coordinate System

Answer 44

North & South celestial pole - point in sky directly about north/south pole on Earth Celestial Equator - circle surrounding earth Ecliptic - a path followed by the sun through the sky over the course of the year. Declination - angle from celestial equator (0^^0), positive UP, negative going DOWN Celestial Prime Meridian - point where sun is located at the vernal equinox (Spring) Right Ascension (RA) - angle (degree) form the celestial "Prime Meridian" (equivalent of celestial longitude)