Geographical Information Systems

Geog 481/506                                                                                                  Tu Th 3:30-4:50pm
Fall 2011                                                                                                          Fillmore 170

Instructor: Ling Bian                                                                                          LabA: Tue:   5-6:20pm, W145, Chunyuan diao
Office: 120 Wilkeson                                                                                        LabB: Thur:  6:30-7:50pm, W145, Tong Sun
Office hours: Tu Th 2-3pm  or by appt.                                                             LabC: Fri:  10-11:20am, W145, Tong Sun

Map Projections and Coordinate Systems

1. Map scale
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., 1:24,000.
        Common map scales:
            1:24,000
            1:250,000
            1: 1,000,000

        Small scale and large scale

        Spatial scales
            map scale
            resolution
            extent

2. Coordinate systems
A system established in relation to (1) a starting point, then the location of every other point can be stated in terms of (2) a defined direction and (3) a distance in the direction.

(1) Spherical coordinate systems
Geographical coordinate systems:
        Great and small circles

        Meridians and parallels

        Latitude
        Measured northward or southward from the equator to poles.
        Ranging 0-90 degrees north or south.
        The measuring units are degrees, minutes, and seconds.
        The length of one degree latitude is similar everywhere, 69miles/111km.

        Longitude
        Measured eastward or westward
        from Prime Meridian at Greenwich, England to the International Date Line
        Ranging 0-180 degrees east or west.
        The measuring units.
        Length of one degree longitude reduces toward poles.

        Reading latitude and longitude
        19⁰50' S: 19 degrees 50 minutes Latitude South
        43⁰50' W: 43 degrees 50 minutes Longitude West

(2) Rectangular coordinate systems
        It converts earth's curved surface onto a flat map surface
        Origin, axes, and measuring unit
        The x value is given first and called easting, then the y value is given and called northing

(i) UTM (Universal Transverse Mercator) coordinates
A rectangular coordinate system for the WORLD

        Measuring unit: meter

        Map projection: Universal Transverse Mercator

        Zones: north-south columns of 6 degrees longitude wide,
        labeled 1 to 60 eastward beginning at the 180 degree meridian

        Rows: east-west rows of 8 degrees latitude high,
        labeled from C to X (without I, O) beginning at 80 degree latitude

        Quadrilaterals

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

        Applications of the UTM system
 

(ii) State Plane coordinates
A rectangular coordinate system for the U.S.
        Measuring unit: feet

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

        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

        The central meridian of a zone is given 2,000,000ft False 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       

        Applications of the State Plane system

3. Topographic maps
Graphical representation of the shape and location of physical features of land and other physical entities. Topographic maps identity elevation of the land in contour lines.

        A map series published by USGS
        It is bound by parallels on the north and south, meridians on the east and west
        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
Geodetic datum:
        are established to provide positional control that supports surveying and mapping projects.
        They cover 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)

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

5. Map projections
A means of converting coordinates on a curved surface to coordinates on a plane.

Map projection vs. coordinate system

A classification of map projections
(1) Classification by conceptual methods
In theory, projections can be created by placing a globe in various positions relative to a light source and a projection surface.

        Cylindrical
        Azimuthal
        Conic

(2) Classification by distortions
The geometrical relationships on the sphere cannot be entirely duplicated on a plane. Angles, areas, distances, and directions are subject to various changes.

        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
 

(3) Commonly used projections
        Transverse Mercator: cylindrical conformal

        Lambert's conformal conic
 

6. Readings Chpt 2