Geographic information systems
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Geographic Information Systems. Coordinate Systems. 1. Map Scale. A ratio between a distance on the map and the corresponding distance on the earth The distance on the map is always expressed as one, e.g., 1 : 100,000 Common map scales 1 : 24,000 1: 100,000 1 : 250,000

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Geographic Information Systems

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Geographic information systems

Geographic Information Systems

Coordinate Systems


1 map scale

1. Map Scale

  • A ratio between a distance on the map and the corresponding distance on the earth

    The distance on the map is always expressed as one, e.g., 1 : 100,000

  • Common map scales

    1 : 24,000

    1: 100,000

    1 : 250,000

    1 : 1,000,000


Map scale

Map Scale

  • Small and large scale

    Which one is a larger map scale?

    1 : 24,000 or 1 : 100,000

  • Spatial scales

    • Map scale (large vs. small)

    • Resolution (fine vs. coarse)

    • Extent (large vs. small)


2 coordinate systems

2. Coordinate Systems

Basic elements of a coordinate system

  • an origin, then the

    location of every

    other point can be

    stated in terms of

  • adefineddirection and

  • a distance in the

    direction


2 coordinate systems1

2 Coordinate Systems

  • Spherical coordinate systems

    Geographic coordinate system

  • Rectangular coordinate systems

    UTM (Universal Transverse Mercator)

    State Plane


2 1 spherical coordinate systems

2 (1) Spherical Coordinate Systems

  • Based on a perfect sphere

  • Geographic coordinate system

    - great circles

    small circles

    - meridians

    parallels

    - Latitude

    - Longitude

courtesy: http://www.colorado.edu/geography/gcraft/


Latitude

Latitude

  • Measured northward or southward from the equator to poles

  • Ranging 0-900 north or south

  • The measuring units are degrees, minutes, and seconds, 10 = 60’ and 1’=60”

  • The length of one degree latitude is similar everywhere, ≈ 111km/69miles


Longitude

Longitude

  • Measured eastward or westward from the Prime Meridian at Greenwich, England to the International Date Line

  • Ranging 0-1800 east or west

  • The measuring units

  • Length of one degree longitude reduces toward poles


Latitude and longitude

courtesy: Mary Ruvane, http://ils.unc.edu/

900 latitude

Lines of Latitude

(East/West - parallels)

Prime

Meridian 00

Lines of Longitude

(North/South - meridians)

Central Parallel 00

Latitude and Longitude


Reading latitude and longitude

Reading Latitude and Longitude

  • 19050’ S: 19 degrees 50 minutes Latitude South

  • 43050’ W: 43 degrees 50 minutes Longitude West

    - 43050’ W


2 2 rectangular coordinate systems

2 (2) Rectangular Coordinate Systems

  • Also referred to as Planar, Cartesian, and Grid coordinate system

  • It converts Earth’s curved surface onto a flat map surface

  • The x value is given first and called easting, then the y value is given and called northing


2 2 i utm

2 (2) (i) UTM

  • Universal Transverse Mercator

    coordinate system

  • A rectangular coordinate

    system for the WORLD

    Gerardus Mercator (1512-1594)

    Courtesy of the Library of Congress, Rare Book Division, Lessing J. Rosenwald Collection.


Utm zones and rows

UTM Zones and Rows

  • Measuring unit: meter

  • Map projection: Universal Transverse Mercator

  • Zones: north-south columns of 60longitude wide, labeled 1 to 60 eastward beginning at the 1800 meridian

  • Rows: east-west rows of 80 latitude high, labeled from C to X (without I, O) beginning at 800 S latitude

  • Quadrilaterals


Utm zones of the world

UTM Zones of the World

courtesy: http://www.colorado.edu/geography/gcraft/


A utm zone

A UTM Zone

  • We always use zones

    and rarely use rows

courtesy: http://www.colorado.edu/geography/gcraft/


Utm easting and northing

UTM Easting and Northing

  • Each of the 60 zones has its own central meridian

  • The central meridian of a zone is given the easting of 500,000m and the equator is given a northing value of 0 for the northern hemisphere

  • For southern hemisphere, the equator is given a northing value of 10,000,000m


Calculate your own zone

Calculate Your Own Zone

44003’ Latitude N, 71058’ Longitude W = Zone ?

courtesy: http://www.colorado.edu/geography/gcraft/


2 2 ii state plane coordinate

2 (2) (ii) State Plane Coordinate

  • A rectangular coordinate system for the UNITED STATES

  • Measuring unit: foot

  • Zones: The U.S. is divided into 120 zones. Zone boundaries follow state and county lines


State plane

State Plane

http://www.cnr.colostate.edu/class_info/nr502/lg3/datums_coordinates/spcs.html


2 2 ii state plane coordinate1

2 (2) (ii) State Plane Coordinate

  • Projections: Each zone has its own projection system

    - Transverse Mercator for states of N-S extent

    - Lambert's conformal conic projection for states of E-W extent


State plane1

State Plane

  • The central meridian of a zone is given 2,000,000ftFalse Easting

  • False origin: it is established in the south and west of the zone as 0, 0

  • False easting, and false northing

  • Zones may overlap    


Difference between systems

Difference between Systems

UTM and many other coordinate systems are defined based on the geographic coordinate system


Difference between systems1

Difference between Systems

  • Try to use the rectangular systems as much as possible, and not to use geographic system for calculation

  • Remotely sensed imagery and digital elevation models routinely use UTM

  • Land record system routinely use State Plane

  • know how to convert between projections (will be discussed in the lab)


3 topographic maps

3. Topographic Maps

  • Planimetric maps

    - Graphical representation of the shape and horizontal location of physical features of land and other physical entities.

  • Topographic maps

    - identity elevation of the land in contour lines.


Topographic maps

Topographic Maps

  • A map series published by USGS

  • It is bound by parallels on the north and south, meridians on the east and west, 7.5’ span in either direction

  • The maps are created from aerial photos

  • The features are topography, vegetation, railroad, streams, roads, urban, etc.

  • Three coordinate systems are marked, geographical, UTM, and State Plane


4 datum

4. Datum

  • Geodetic datum: are established to provide positional control that supports surveying and mapping projects covering large geographic areas, such as a country, a continent or the whole world

    North American Datum of 1927 (NAD27)North American Datum of 1983 (NAD83)

  • Coordinates change if datum changes: a control point in CA

    On NAD83: -117 12 57.75961, 34 01 43.77884

    On NAD27: -117 12 54.61539, 34 01 43.72995


Datum

Datum

  • Vertical datum: is the zero surface from which all elevations or heights are measured


5 map projections

5. Map Projections

  • A means of converting coordinates on a curved surface to coordinates on a plane

  • Map projections vs. coordinate systems

    - Map projections define how positions on the earth’s curved surface are transformed onto a flat map surface

    - Coordinate systems superimposed on the surface to provide a referencing framework on which positions are measured


Map projections

Map Projections

  • A classification of map projections

  • By conceptual methods

    Cylindrical, Azimuthal, and Conic

  • By distortions

    Conformal, Equal-area, Equidistant, and Azimuthal


Map projections by methods

Map Projections – by Methods

  • Cylindrical

    1. Mercator 2. Transverse Mercator

    http://exchange.manifold.net


Map projections by methods1

Map Projections - by Methods

  • Azimuthal

  • Conic

    http://exchange.manifold.net


Map projections by methods2

Map Projections - by Methods

http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html


Map projections by distortions

Map Projections - by Distortions

  • Conformal projections  It retains shapes about a point

  •  Equal-area projections  It retains correct relative size

  •  Equidistant projections  It retains uniform scale in all directions but only from one or two points

  •  Azimuthal projections  It retains correct directions from one or two points


Map projections by distortions1

Map Projections - by Distortions

courtesy: Mary Ruvane, http://ils.unc.edu/

Conformal –

preserves shape

Equivalent -

preserves area

Equivalent -

preserves area

Compromise -

preserves neither


Commonly used projections

Commonly Used Projections

  • Transverse Mercator: cylindrical conformal

  •  Lambert's conformal conic

    http://www.youtube.com/watch?v=b1xXTi1nFCo&feature=player_embedded

    http://www.youtube.com/watch?v=AI36MWAH54s


Commonly used projections1

Commonly Used Projections

  • UTM as a coordinate system

  • UTM as a means of projection


Readings

Readings

  • Chapter 2


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