Questions and Answers

Questions and Answers

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

a defined direction 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: 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 Latitude and Longitude Lines of Latitude 900 latitude (East/West - parallels) Prime

Meridian 00 Lines of Longitude (North/South - meridians) courtesy: Mary Ruvane, Central Parallel 00 Reading Latitude and Longitude

42053 N: 42 degrees 53 minutes Latitude North 78053 W: 78 degrees 53 minutes Longitude West 2 (2) Rectangular Coordinate Systems Also referred to as Planar, Cartesian, and Grid coordinate system It converts Earths 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 (1512-1594) Gerardus Mercator 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 60 longitude 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:

A UTM Zone We always use zones and rarely use rows courtesy: 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

671,000m Easting, 4,749,000m Northing Calculate Your Own Zone 44003 Latitude N, 71058 Longitude W = Zone ? courtesy: 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

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 2,000,000ft 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 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. Datum Vertical datum: is the zero surface from which all elevations or heights are measured 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

4. 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 earths 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

Map Projections - by Methods Azimuthal Conic 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 Conformal preserves shape Equivalent preserves area Equivalent preserves area Compromise preserves neither

courtesy: Mary Ruvane, Commonly Used Projections Transverse Mercator: cylindrical conformal Lambert's conformal conic ature=player_embedded Commonly Used Projections

UTM as a coordinate system TM as a means of projection Readings Chapter 2 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

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