8/8/2019 Topographic Landsat Maps Lecture

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Topographic Maps, AerialPhotos and Satellite

Images(Or things that are really

useful whether you’re intogeology or not!)

8/8/2019 Topographic Landsat Maps Lecture

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The Basics: What is atopographic map?

• A 2-D model of 3-D landscape

• Relief – difference in elevation (i.e.valleys, peaks, coastlines, etc)

– Contour lines – represent elevations

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Latitude

• “Latitude is fat-itude”

• Measured in degrees

•

From 0° to 90°N or 90°S– What do those represent?

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Longitude

• Also measure in degrees

• Degrees east or west of the primemeridian

– Runs from N to S through Greenwich,UK 

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Breaking down degrees…..

• 1 degree   60 min (‘)   60 sec (“)

• Quadrangle – Section of earthbounded by latitude and longitude

• 15 minute quadrangle

• 7.5 minute quadrangle

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North

 450mi from TrueNorth

–Declination Difference in

degrees

 True north based ongeography

 Magnetic North shifts on the

’earth s magnetic

 field due to( )metallic iron core

 What does this mean for map accuracy?

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Symbols

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 Digital Terrain Models

-Constant altitude flight-Overlapping radar pulses-    –Similar elevation similar color

 Why do you have to be above?

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Making the map from aerialview

• Eliminate angular distortion

• Ground truth – check elevations onthe ground!

– How would you do this?

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• Contour lines connect all points thathave the same elevation above sealevel

• Index contours – elevations printed

• Contour interval – specified on mapas the regular change betweenelevations

• Fig. 9.3 – What’s the contour

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RULES! (And guidelines…)

• Contour lines NEVER cross? (Thinkabout why….)

• Contour lines ALWAYS close to form acircle (unless you are going off themap)

• The tip of a V-shaped notched

ALWAYS points uphill

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Contour Lines (Fig 9.6)•

Can estimate elevation between twopoints

• Even-spaced contours of different

elevations tell us something aboutslope!

• Line can show steep vs. gentle slope

•

Depression contours – closed circlewith hachure marks on the downhillside

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Reading contour lines

• Fig 9.7

• What is the elevation of the middlehill?

• What cardinal direction is downhill onthe valley river?

• What is the easiest route up to theridge point?

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Benchmark

• i.e. BM 463 – Permanent marker withknown elevation

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Scales of Maps and Models

• Ratio scale

• 1:50, 1:24,000, etc (Always sameunits)

• Think of zooming in and out!

• Convert!

– 1:24,000 – 1in is 24,000in

– 24,000in is 2000ft

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GPS• 28 satellites,

• 12-hour orbit

• Uses foursatellites

and a receiverto triangulate

• Usually anaccuracy of 

10-15m• Idea is 4 sats

are 15° abovethe horizonanywhere at

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UTM – Universal TransverseMercator System

• Rectangular grid in meters

• 60 N-S zones – Zone 01 to Zone 60

•

Easting – measured in meters E of Wedge

• Northing – distance from equator inmeters

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Today’s Lab…..

• Complete the questions aboutvarious topo quadrangles

• Draw your own topo map

– PART I

– PART II