The Nature of Maps
Portraying Earth
•
•
•
•
•
•
The Nature of Maps
Map Projections
Isolines-(contour lines) of equal elev.
Global Positioning System (GPS)
Remote Sensing
Geographic Information Systems (GIS)
Figure 2-1
Map Scale
• Types of Scale
Examples
of Map
Scales
– Graphic Scale
– Verbal Scale
– Representative Fraction
• Large and Small Scale
Small-scale map
portrays large area;
large-scale map
shows small area in
greater detail
Figure 2-3
Map Projections
•
•
•
•
•
Conic Projection
Conic
Plane
Cylindrical
Interrupted
Mercator
Map projections transform rounded surface of the Earth to display on
a flat map
Figure 2-6
1
Cylindrical Projection
Plane Projection
Figure 2-7
Figure 2-8
Equivalence Versus Conformality
Interrupted Projection
Portrays some areas more accurately at expense of other areas Figure 2-9
The Mercator Projection
Emphasizes “equal
areas”
Emphasizes shapes and angular relationships
Figure 2-10
Isolines –
or contour
lines show
elevation
Santa Paula CA, 1:62,500; CI= 20’
Figures 2-B, 2-C
Contour interval is
the change in
elevation from line
to line
2
Isolines
Average
Annual
Precipitation
Figure 2-13a
Remote Sensing
Global Positioning System (GPS)
•
•
•
•
•
Aerial Photographs
Orthophoto Maps
Color and Color-Infrared Sensing
Thermal Infrared Sensing
Microwave, Radar, Radar inteferometry and
Sonar Sensing
• Multispectral Remote Sensing
• LIDAR (light IR detection and ranging)
• Misc. geophysical imagery (gravity, magnetics,
etc)
Figures 2-16
Aerial Photographs
Sequenced overlapping photos allow
stereo viewing. Combined use with
surveying on land allowed construction
of topo maps at 1:24,000 scale for the
conterminous US by 1984.
Orthophoto
Maps
Orthophotos have
been georeferenced,
or adjusted to fit
accurately to the
mapped coordinate
system.
Figure 2-20
Figure 2-18
3
Radar interfereometry—detects land shifts from high up
Radar Sensing
Topographic map of
Australia. Colors
represent elevations
and include
bathymetry.
http://vulcan.wr.usgs.gov/home.html
http://www.panga.cwu.edu
/
GPS data below
shows the uplift is
real; ~1 in per year
over 10 mi area!
GPS stations
West Sister uplift
Figure 2-24
Central Oregon Cascades
Examples of remote sensing
Multispectral
Remote
Sensing
Landsat Images
Mosaic of landsat images of
Iberian Peninsula and
surrounding areas.
Geographic
Information
Systems (GIS)
LIght Detection And Ranging
• Airborne scanning laser
rangefinder
• Differential GPS
• Inertial Navigation
System
-layers of spatial data
superimposed upon one
another.
30,000 points per second
at ~15 cm accuracy
-layers can be turned off,
individually enhanced, or
made translucent.
-“Geoprocessing” is
analyizing one layer
based on another.Figure 2-29
• $400–$1000/mi2,
106 points/mi2, or
0.04–0.1 cents/point
LIDAR
Extensive filtering to
remove tree canopy
(virtual defor-estation)
4
1:24,000 topo map of portion of
Bainbridge Island
10-meter DEM from contours of
the same area of Bainbridge
Island
Picture:Southern
Oblique
tip ofview
Bainbridge
of S
Island
end
Rockaway Beach
12-ft DEM from LIDAR
Modern wave-cut
bench
Southern tip of Bainbridge Island
High-resolution LIDAR
topography of the same
area as previous slide
Wave-cut bench uplifted
20 ft by Seattle Fault
900–930 AD.
• Fly in winter, when leaves are off
• Near-infrared laser; doesn’t penetrate clouds,
rain
• Errors
Largest are in angles—up to 1 m x-y error
Ranging error = ~15 cm z error!
• 2/3 of surveyed points on trees and buildings;
remove with automatic geometric filtering
• Multiple reflections from one laser pulse
= better filtering
5
• Optimum working distance circa 1 km
– Adequate reflection brightness
– Keep laser eye-safe
• Spot diameter: decimeters to meters
• Spot spacing: 1 to 5 meters
• Multiple passes
Why is LIDAR better than photogrammetry?
(It’s the trees)
Suppose timber allows 1 of
3 arbitrary rays to reach
ground; 1/3 of ground can
be surveyed by LIDAR
Photogrammetry requires
2 separate views of a
point; only 1/9 of ground
will be locatable
– multiple look angles
– higher point density
– internal consistency check
• $400 - $1,000 / mi2
Uses for high-resolution
topography
landslides
Toejam fault not visible
before lidar!
Examples of maps made
with Arcview GIS software
by ESRI.
• Finding faults (earthquake frequency,
kinematics)
• Geologic mapping
• Landslide hazards
• Flood hazards, groundwater infiltration, runoff
modelling
http://pugetsoundlidar.ess.washi
• Fish habitat
ngton.edu/
? Precision forestry
? Noise propagation
Below:
orthophoto atop
DEM for Mud
Bay, Eld Inlet
Mud Bay in Eld
Inlet at low low tide.
Dots show
submerged forest
Southern
Puget Sound
submerged
trees
6
Nisqually River
Lidar images
delta area lidar
I-5
esker
kettles
7