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## 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 1 : 1,000,000**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**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 Systems**• Spherical coordinate systems Geographic coordinate system • Rectangular coordinate systems UTM (Universal Transverse Mercator) State Plane**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**• 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**• 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**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**• 19050’ S: 19 degrees 50 minutes Latitude South • 43050’ W: 43 degrees 50 minutes Longitude West - 43050’ W**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**• 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**• 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**courtesy: http://www.colorado.edu/geography/gcraft/**A UTM Zone**• We always use zones and rarely use rows courtesy: http://www.colorado.edu/geography/gcraft/**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**44003’ Latitude N, 71058’ Longitude W = Zone ? courtesy: http://www.colorado.edu/geography/gcraft/**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**http://www.cnr.colostate.edu/class_info/nr502/lg3/datums_coordinates/spcs.html**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 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**UTM and many other coordinate systems are defined based on the geographic coordinate system**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**• 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**• 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**• 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**• 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 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**• A classification of map projections • By conceptual methods Cylindrical, Azimuthal, and Conic • By distortions Conformal, Equal-area, Equidistant, and Azimuthal**Map Projections – by Methods**• Cylindrical 1. Mercator 2. Transverse Mercator http://exchange.manifold.net**Map Projections - by Methods**• Azimuthal • Conic http://exchange.manifold.net**Map Projections - by Methods**http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html**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 Distortions**courtesy: Mary Ruvane, http://ils.unc.edu/ Conformal – preserves shape Equivalent - preserves area Equivalent - preserves area Compromise - preserves neither**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 Projections**• UTM as a coordinate system • UTM as a means of projection**Readings**• Chapter 2