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
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


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


    - Latitude

    - Longitude



  • 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


  • 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,

900 latitude

Lines of Latitude

(East/West - parallels)


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


A utm zone
A UTM Zone

  • We always use zones

    and rarely use rows


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 ?


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

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


  • 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

Map projections by methods1
Map Projections - by Methods

  • Azimuthal

  • Conic

Map projections by methods2
Map Projections - by Methods

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,

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

Commonly used projections1
Commonly Used Projections

  • UTM as a coordinate system

  • UTM as a means of projection


  • Chapter 2