1 Representations of the Earth Maps, GIS and Remote Sensing.

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Representations of the Representations of the EarthEarth

Maps, GIS and Remote Maps, GIS and Remote SensingSensing

© Vicki Drake© Vicki Drake 22

The first Lines of Parallel and The first Lines of Parallel and MeridiansMeridians


LATITUDE AND LONGITUDELATITUDE AND LONGITUDELines of Parallel equate to Latitude.

Latitude is measured from the equator to the poles (00 – 900)

Lines of Meridians equate to Longitude.

Longitude is measured from the Prime Meridian (00) to International Date Line (1800 E/W)


Coordinate Systems –Latitude Coordinate Systems –Latitude and Longitudeand Longitude


MEASURING LATITUDEMEASURING LATITUDE• The equator is a Great Circle: dividing the The equator is a Great Circle: dividing the

earth into two equal halvesearth into two equal halves• Lines of latitude are parallel and evenly Lines of latitude are parallel and evenly

spaced: a degree of latitude represents a spaced: a degree of latitude represents a constant distance on the ground.constant distance on the ground.– Approximately 69 miles (111 kilometers)Approximately 69 miles (111 kilometers)

• These lines of parallels are measured in These lines of parallels are measured in angular degrees (°). angular degrees (°). – There are 90 angular degrees of latitude There are 90 angular degrees of latitude

from the equator to each of the poles. from the equator to each of the poles. – The equator has an assigned value of 0°. The equator has an assigned value of 0°. – Measurements of latitude are also Measurements of latitude are also

defined as being either north or south of defined as being either north or south of equator to distinguish the hemisphere of equator to distinguish the hemisphere of their locationtheir location


MEASURING LONGITUDEMEASURING LONGITUDE• All lines of longitude can be “Great Circles”All lines of longitude can be “Great Circles”• Lines of longitude or meridians are non-parallel circular arcs Lines of longitude or meridians are non-parallel circular arcs

that meet at the poles. that meet at the poles. – At the equator, a degree of longitude measures At the equator, a degree of longitude measures

approximately 69 miles (111 kilometers)approximately 69 miles (111 kilometers)– At 40At 4000 N or S, a degree of longitude measures N or S, a degree of longitude measures

approximately 53 miles (85 kilometers)approximately 53 miles (85 kilometers)– At the poles, a degree of longitude measures 0 miles or At the poles, a degree of longitude measures 0 miles or

kilometers – all meridians converge to a single ‘point’ at kilometers – all meridians converge to a single ‘point’ at the north or south polethe north or south pole

• There are 180° of longitude either side of a starting meridian There are 180° of longitude either side of a starting meridian which is known the Prime Meridian. which is known the Prime Meridian. – The Prime Meridian has a designated value of 0°. The Prime Meridian has a designated value of 0°. – The Prime Meridian starts at Royal Observatory, The Prime Meridian starts at Royal Observatory,

Greenwich, London, EnglandGreenwich, London, England• Measurements of longitude are also defined as being either Measurements of longitude are also defined as being either

west or east of the Prime Meridian.west or east of the Prime Meridian.• The maximum value that a meridian of longitude can have is The maximum value that a meridian of longitude can have is

180° which is the distance halfway around a circle. 180° which is the distance halfway around a circle. – This meridian is called the International Date Line. This meridian is called the International Date Line. – Designations of west and east are used to distinguish Designations of west and east are used to distinguish

where a location is found relative to the Prime Meridian.where a location is found relative to the Prime Meridian.• For example, all of the locations in North America have For example, all of the locations in North America have

a longitude that is designated west. a longitude that is designated west.


Projections--Going from 3D Projections--Going from 3D to Flat Mapsto Flat Maps


Projections—From a Sphere to Flat Maps

Projections are created by transferring points on the earth onto a Projections are created by transferring points on the earth onto a flat surface. You can think of this as having a light in the middle of flat surface. You can think of this as having a light in the middle of the earth, shining through the earth’s surface, onto the projection the earth, shining through the earth’s surface, onto the projection surface. There are three basic methods for doing this:surface. There are three basic methods for doing this:

Cylindrical--projection surface wrapped around the Earth; point of Cylindrical--projection surface wrapped around the Earth; point of contact is equatorcontact is equator

Conformal projection (‘preserves’ shape of continents at equator Conformal projection (‘preserves’ shape of continents at equator only)only)

Planar--projection surface is a ‘flat’ surface against the Earth at a Planar--projection surface is a ‘flat’ surface against the Earth at a particular latitude or longitudeparticular latitude or longitude

NeitherNeither Conformal or Equal Area Conformal or Equal Area Does not ‘preserve’ shape of continents nor provide measure Does not ‘preserve’ shape of continents nor provide measure

for equal areafor equal area

Conic–- projection surface is a cone is placed on or through the Conic–- projection surface is a cone is placed on or through the surface of the Earthsurface of the Earth

Where the projection surface touches the Earth is the “Standard Where the projection surface touches the Earth is the “Standard Line.”Line.”

Can be Can be eithereither Conformal or Equal Area Conformal or Equal Area


Trouble with ProjectionsTrouble with Projections Distortion--It is impossible to flatten a round object without Distortion--It is impossible to flatten a round object without

distortion.distortion.

Projections try to preserve one or more of the following Projections try to preserve one or more of the following properties:properties:

Area--sometimes referred to as equal area (for small areas)Area--sometimes referred to as equal area (for small areas) Projections that preserve ‘area’ are referred to as “Equal Area” Projections that preserve ‘area’ are referred to as “Equal Area”

projectionsprojections

Shape--usually referred to as “conformality”, again for small Shape--usually referred to as “conformality”, again for small sectionssections

Projections that preserve “shape” are referred to as “Conformal” Projections that preserve “shape” are referred to as “Conformal” projectionsprojections

Direction--or “azimuthality” - cardinal directions (N,S,E,W)Direction--or “azimuthality” - cardinal directions (N,S,E,W)

Distance – a difference in distance between two points on the Distance – a difference in distance between two points on the Earth and same two points represented on mapEarth and same two points represented on map


PROJECTION CHALLENGESPROJECTION CHALLENGES• Conformality Conformality

– When the scale of a map at any point on the map is the same in When the scale of a map at any point on the map is the same in any direction, the projection is conformal. any direction, the projection is conformal.

• Meridians (lines of longitude) and parallels (lines of latitude) intersect Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angles.at right angles.

• Shape is preserved locally on conformal maps. Shape is preserved locally on conformal maps.

• Distance Distance – A map is equidistant when it accurately portrays distances from A map is equidistant when it accurately portrays distances from

the center of the projection to any other place on the map. the center of the projection to any other place on the map. • Direction Direction

– A map preserves direction when azimuths (angles from a point A map preserves direction when azimuths (angles from a point on a line to another point) are portrayed correctly in all on a line to another point) are portrayed correctly in all directions. directions.

• Area Area – When a map portrays areas over the entire map so that all When a map portrays areas over the entire map so that all

mapped areas have the same proportional relationship to the mapped areas have the same proportional relationship to the areas on the Earth that they represent, the map is an equal-area areas on the Earth that they represent, the map is an equal-area map. map.

• Scale Scale – Scale is the relationship between a distance portrayed on a map Scale is the relationship between a distance portrayed on a map

and the same distance on the Earth. and the same distance on the Earth.

• CONFORMAL VS EQUAL AREA: Projections can be either CONFORMAL VS EQUAL AREA: Projections can be either conformal or equal area – but not both!conformal or equal area – but not both!


Projections--Cylindrical Projection

Point of contact at equator


Projections--”Developing” a Cylindrical Projection


Cylindrical Projection: A Cylindrical Projection: A Conformal ProjectionConformal Projection

Note increasing distance between lines of latitude….why?


Why Mercator? Why Mercator? NAVIGATION!!NAVIGATION!!• In a Mercator projection, the lines of longitude are In a Mercator projection, the lines of longitude are

straight vertical lines equi-distance apart at all straight vertical lines equi-distance apart at all latitudes, and horizontal distances are stretched latitudes, and horizontal distances are stretched above and below the equator.above and below the equator.

• This stretching is exaggerated near the poles This stretching is exaggerated near the poles – The Mercator projection mathematically stretches The Mercator projection mathematically stretches

vertical distances by the same proportion as the vertical distances by the same proportion as the horizontal distances so that shape and direction are horizontal distances so that shape and direction are preservedpreserved

– Shape is preserved….what happens to the measurement Shape is preserved….what happens to the measurement of area?of area?

• Mercator’s projection preserves exactly what Mercator’s projection preserves exactly what sailors in the 16sailors in the 16thth century needed -- shapes and century needed -- shapes and directions; they were very willing to accept the directions; they were very willing to accept the size distortion.size distortion.

• Any straight line drawn between two points Any straight line drawn between two points on a Mercator Projection represents a on a Mercator Projection represents a “rhumb line” – true compass direction“rhumb line” – true compass direction


Rhumb Line – True Compass Rhumb Line – True Compass Heading: Mercator ProjectionHeading: Mercator Projection

Mercator Projection was the navigation map for sailing ships: good direction but longest route


MERCATOR PROJECTIONMERCATOR PROJECTION• The normal aspect of the Mercator The normal aspect of the Mercator

projection showing the great circle projection showing the great circle between Miami and Tokyobetween Miami and Tokyo– Great Circles are the shortest distance Great Circles are the shortest distance

between two points on a globebetween two points on a globe

Shortest distance, but not true compass headings


Projections--Polar Planar Projection


Polar Planar ProjectionPolar Planar Projection

Projection centered on North Pole


Planar Projection: GnomonicPlanar Projection: GnomonicGnomonic projections can be either “Conformal” or “Equal Area”, but not both


Gnomonic ProjectionGnomonic Projection


NAVIGATION: GNOMONICNAVIGATION: GNOMONIC• Any straight line Any straight line

drawn on a drawn on a gnomonic projection gnomonic projection is an Arc of a Great is an Arc of a Great Circle Route – Circle Route – shortest distance shortest distance between two points between two points on a globeon a globe– Great circles are Great circles are

represented by represented by straight lines, making straight lines, making it very useful in it very useful in plotting great circle plotting great circle routes between routes between arbitrary destinations arbitrary destinations

• Gnomonic Maps are Gnomonic Maps are the navigational the navigational maps for “air” agemaps for “air” age

Straight line between two points on map is shortest distance


Projections--Conic Projection


Conic Conformal ProjectionConic Conformal Projection


CONIC PROJECTIONSCONIC PROJECTIONS

• A better choice for mapping regions A better choice for mapping regions such as the United States is a such as the United States is a conicconic projection, which projects shapes projection, which projects shapes from the Earth’s sphere onto a cone.from the Earth’s sphere onto a cone.

• Locations near the line where the Locations near the line where the cone is tangent to the Earth will be cone is tangent to the Earth will be relatively free of distortionrelatively free of distortion


PROBLEMS WITH CONIC PROJECTIONSPROBLEMS WITH CONIC PROJECTIONS

Projection Distortion--shown with a conic projection cutting through the earth’s surface at 2 parallels


PROJECTION WOES!PROJECTION WOES!


MAP SCALEMAP SCALE

• Map Scale is the ratio of the distance Map Scale is the ratio of the distance between two points on the Earth’s surface between two points on the Earth’s surface and the distances between corresponding and the distances between corresponding points on a mappoints on a map

• There are several types of map scales:There are several types of map scales:– Verbal Scale: 1 inch = 1 mileVerbal Scale: 1 inch = 1 mile– Bar Scale: a graph depicting distancesBar Scale: a graph depicting distances

– Representative Fraction:Representative Fraction:• One unit of measured distance on a map equal some One unit of measured distance on a map equal some

units of measured distance in the real worldunits of measured distance in the real world


REPRESENTATIVE FRACTIONREPRESENTATIVE FRACTION• Representative Fraction (RF) is the ratio Representative Fraction (RF) is the ratio

between measured distances on a map and between measured distances on a map and measured distances on the Earth’s surface.measured distances on the Earth’s surface.

• RF is a unitless measure – however, both RF is a unitless measure – however, both sides of the ratio must be identical unitssides of the ratio must be identical units

• A RF scale expressed as a ratio of 1:25,000 A RF scale expressed as a ratio of 1:25,000 means that one unit of distance measured means that one unit of distance measured on the map represents 25,000 identical on the map represents 25,000 identical units of distance on the ground (‘in the real units of distance on the ground (‘in the real world’). world’). – 1 inch measured on a map represents 25,000 1 inch measured on a map represents 25,000

inches on the Earth’s Surface or… inches on the Earth’s Surface or… – 1 cm measured on a map represents 25,000 1 cm measured on a map represents 25,000

centimeters on the Earth’s surface.centimeters on the Earth’s surface.


LARGE-SCALE VS SMALL-LARGE-SCALE VS SMALL-SCALESCALE• Large-Scale Maps show very small portions Large-Scale Maps show very small portions

of the real world, but with great detail. of the real world, but with great detail. – Large-Scale maps have small denominators Large-Scale maps have small denominators

i.e., 1:12,000 or 1:10,000i.e., 1:12,000 or 1:10,000– Topographic maps are examples of large-scale Topographic maps are examples of large-scale

mapsmaps

• Small-Scale maps show very large portions Small-Scale maps show very large portions of the real world, but with minimal detailof the real world, but with minimal detail– Small-scale maps have large denominators, Small-scale maps have large denominators,

i.e., 1:100,000 or 1:1,000,000i.e., 1:100,000 or 1:1,000,000– Wall maps are examples of small-scale mapsWall maps are examples of small-scale maps


LARGE SCALE VS. SMALL LARGE SCALE VS. SMALL SCALESCALE


Very Early Maps!Very Early Maps!

Town Plan from Catal Hyük, Town Plan from Catal Hyük, Anatolia (6200 B.C.) Anatolia (6200 B.C.)

Reconstruction of DrawingReconstruction of Drawing


Early MapsEarly Maps

• Clay tablets from Clay tablets from Ga-SurGa-Sur

2500 B.C.2500 B.C.

Interpretation of Interpretation of drawingdrawing


Early World MapsEarly World Maps• The world according to Herodotus 450 BCThe world according to Herodotus 450 BC


Early World MapEarly World Map• Reconstruction of world map according to Dicaearchus (300 Reconstruction of world map according to Dicaearchus (300

B.C.)B.C.)


Babylonian Clay Map and Babylonian Clay Map and Interpretation – 600ADInterpretation – 600AD


Topographic MapsTopographic Maps


3-D Topographic Maps3-D Topographic Maps


Temperature MapsTemperature Maps


Ethnicity MapsEthnicity Maps


Sea Floor MapsSea Floor Maps


Precipitation MapsPrecipitation Maps


Population MapsPopulation Maps


COMPUTER MAPPING: GISCOMPUTER MAPPING: GIS

•GIS, Geographic Information Systems, are a way to visualize, manipulate, analyze and display spatial and non-spatial data– Spatial data is geo-referenced– Non-spatial data is descriptive

•A spatial database (“geodatabase”) is used


GIS is an Integrating GIS is an Integrating TechnologyTechnology


HOW DO GIS USE HOW DO GIS USE DATABASES?DATABASES?

• Geodatabases provide geo-Geodatabases provide geo-referenced and descriptive data for referenced and descriptive data for analysisanalysis


Cities use GIS to locate Cities use GIS to locate vulnerable pipelinesvulnerable pipelines


Parcels in 100-year Flood Parcels in 100-year Flood ZoneZone


Income Maps – Census Income Maps – Census tractstracts


Earthquake Maps - Earthquake Maps - LocationsLocations


Earthquake Maps – FaultsEarthquake Maps – Faults


Southern California Earthquakes, 2000- Creating Density Maps


3-Dimensional Symbolization 3-Dimensional Symbolization of Data (using 3-D Analyst)of Data (using 3-D Analyst)


Remote Sensing and MapsRemote Sensing and Maps


Remote Sensing PlatformsRemote Sensing Platforms


• Typical Remote Typical Remote Sensing Sensing Platforms used Platforms used todaytoday


Remote Sensing uses Remote Sensing uses EnergyEnergy


Spectral SignaturesSpectral SignaturesAll objects (natural or synthetic) reflect and emit electromagnetic radiation over a range of wavelengths characteristic of the object. Distinctive reflectance and emittance properties are the spectral signatures of object

Remote sensing depends upon operation in wavelength regions of spectrum where these spectral signatures occur for identification purposes.


Space-based Remote SensingSpace-based Remote Sensing• When the sun’s energy passes through the When the sun’s energy passes through the

atmosphere, three reactions can occur:atmosphere, three reactions can occur:– Transmission Transmission – ReflectionReflection– Scattering Scattering – AbsorptionAbsorption


Spatial Resolution – by pixelSpatial Resolution – by pixel

MODIS: 250meters x 250meters

Landsat: 30meters x 30meters

IKONOS: 1meter x 1meter


Sample Landsat TM image along Sample Landsat TM image along Missouri RiverMissouri River

1 Representations of the Earth Maps, GIS and Remote Sensing.

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