Maps & GIS

Report
Maps and GIS
Created by Lisa Bingham
University of Stavanger, Norway
Course Objectives
• Read, understand, and interpret maps
• Basic understanding of GIS
• Basic understanding of GPS
http://img.moonbuggy.org/theroad-to-success/
Reading a map
Reading maps
• Maps relate information
– It is up to the viewer to interpret the information
– How?
• Investigate the map
– Identify the parts of the map
– Familiarize yourself with the map
– Are there graphs? Inset maps? Additional figures?
– What is the purpose of the map? What does the
map tell you? What information does it relate?
What makes a “good” map?
• Defined purpose and audience.
– These influence what makes a “good” map for the
intended audience.
– tourist vs. geologist
• Avoid cluttering or over-complications
• Legible labeling
• Coloring and patterns should follow
cartographic conventions.
Features of a map
•
•
•
•
A concise map title
An easy to read scale bar
An easy to read legend, if necessary
North arrow if the coordinate system is not
clear or if the map is turned to an angle
• Legible coordinates at the border of the map
• Projection information
Identify
the parts
of a map
Locate:
•Title
•Scale
•Scale bar
•Legend
•Coordinate system
or grid markings
•Location or inset map
•Publication information
Where is the title?
Title
Where is the legend?
Where is the inset map?
Where is the scale bar?
Scale
Scale
bar
Where is the scale?
Where are the grid coordinates?
Where is the north arrow?
Where is the publication information?
Compiler and
publication information
Where are the graphs?
Legend
Inset map
Graphs
Some maps have
north arrows or
compass roses, or
may include
projection
information. This
map does not.
Grid
coordinates
Familiarize
yourself
with the
map.
What does
the map
tell you?
Mineral-rich in the north
Mineral-poor in the center
Minerals in the south
Diamonds with gold
in the northeast
Gold in north-central
If you represented a
mining company,
where would you look
for:
•gold?
•diamonds?
•bauxite?
•radioactive minerals?
Mica-rich in the south
Diamond production decreasing
Understanding Map Scales
• Representations:
– verbal (1 map centimeter represents 30,000 ground
centimeters)
– fraction (1:25,000)
– graphic (scale bar)
• Map scale indicates how much a given distance was
reduced to be represented on the map.
Understanding Map Scales
• Small-scale map
depicts large areas, so
low resolution.
• 1:10,000,000
Understanding Map Scales
• Large-scale map depicts
small areas, so high
resolution.
• 1:50,000
• 1,267 inches to 1 mile
Small-scale vs. Large-scale Maps
• When the scale is written as a fraction, is the
fraction very small or very large?
– 1/1,000
– 1/100,000
– 1/1,000,000
– 1/5,000,000
– 1/10,000,000
• Identifying a map as small- or large-scale is an
exercise of relativity
Reading Map Contours
• First familiarize yourself with the map
• Locate the contour interval
• Investigate the contours
– Are they close together? Far apart?
– Are the very straight?
– Are there many concentric circles?
– Do the contours shape like V’s or U’s?
Elevation Contour
What can be said about the
elevation in this area (northeast
corner of the previous map)?
What can be said about the
elevation in this area (northeast
corner of the previous map)?
V
shape
Steep
slopes
Coastline
V
shape
Less steep
area
What can be said about the elevation in
this area (central area of the large map)?
What can be said about the elevation in
this area (central area of the large map)?
Flat area
Coastline
Flat area
High point or
depression?
Steeper area
with very curvy
contours
High point or
depression?
High
point
Understanding Coordinate
Systems
What is a coordinate system?
•
•
A mathematical system used to explain the location
of a point on the earth (or other planet).
A geographic coordinate system is used to assign
geographic locations to objects.
–
•
A global coordinate system of latitude-longitude is one
such framework.
Another is a planar or Cartesian coordinate system
derived from the global framework.
Latitude facts:
 Lines of latitude (parallels) are evenly
o
o
spaced from 0 at equator to 90 at poles.
o
 60 nautical miles (~ 110 km)/1 , ~1.8
km/minute and ~ 30 m/second of latitude.
 N. latitudes are positive,
S. latitudes are negative.
Equator
From M. Helper, University of Texas, 2008
Longitude facts:
 Lines of longitude (meridians)
converge at the poles; the distance of
a degree of longitude varies with
latitude.
180o
 Zero longitude is the Prime
(Greenwich) Meridian (PM);
longitude
o
is measured from 0-180 east and
west of the PM.
 East longitudes are positive,
West longitudes are negative.
P.M.
From M. Helper, University of Texas, 2008
Units of Measure
• Decimal degrees (DD), e.g. - 90.50o, 35.40o
– order by longitude, then latitude
– Format used by ArcGIS software
• Degrees, Minutes, Seconds (DMS), e.g. – 90o
30’ 00”, 35o 24’ 00”
From M. Helper, University of Texas, 2008
What is a map projection?
 A map projection is used to portray all or part of
the round Earth on a flat surface. This cannot be
done without some distortion.
 Every projection has its own set of advantages and
disadvantages. There is no "best" projection.
 The mapmaker must select the one best suited to
the needs, reducing distortion of the most
important features.
Laying the earth flat
• Why?
– Need convenient means of measuring and comparing
distances, directions, areas, shapes.
– Traditional surveying instruments measure in meters or
feet, not degrees of longitude and latitude.
– Globes are bulky and can’t show detail.
• 1:24,000 globe would have diameter of ~ 13 m
• Typical globe has scale of ~ 1:42,000,000
– Distance & area computations more complex on a sphere.
From M. Helper, University of Texas, 2008
Laying the earth flat
• How?
– Using projections – transformation of curved earth to a
flat map; systematic rendering of the longitude and
latitude graticule to rectangular coordinate system.
Scale
1: 42,000,000
Scale Factor (for specific points)
0.9996
Map
Earth
Globe
Globe distance
Earth distance
Map distance
Globe distance
Mercator Projection
From M. Helper, University of Texas, 2008
Inflatable globe demonstration
Blown up
and
Cut up
Laying the earth flat
• Systematic rendering of Latitude (f) &
Longitude (l) to rectangular (x, y) coordinates:
y
0, 0
Geographic Coordinates
(f, l)
x
Projected Coordinates
(x, y)
Map Projection
From M. Helper, University of Texas, 2008
Laying the earth flat
• “Geographic” display – no projection
– x = l, y = f
– Grid lines have same scale and spacing
y
f
x
l
From M. Helper, University of Texas, 2008
“Geographic” Display
• Distance and areas distorted by varying amounts
(scale not true); e.g. high latitudes
f
y
l
x
From M. Helper, University of Texas, 2008
Projected Display
• E.g. Mercator projection:
– x=l
– y = ln [tan f + sec f]
90
f
00
y
5+
From M. Helper, University of Texas, 2008
Laying the earth flat
• How?
Projection types:
Orthographic
a
Gnomonic
A’
T
T’
B’
b
a
T
b
Stereographic
A’
T’
B’
A’
a
T
b
T’
B’
From M. Helper, University of Texas, 2008
Inflatable globe demonstration
Light shines through
Projection produces distortion of:
•
•
•
•
Distance
Area
Angle
Shape
Distortions vary with scale; minute for large-scale maps
(e.g. 1:24,000), gross for small-scale maps (e.g. 1:
5,000,000)
Goal: find a projection that minimizes
distortion of property of interest
From M. Helper, University of Texas, 2008
How do I select a projection?
• Scale is critical – projection type makes very little
difference at large scales
• For large regions or continents consider:
– Latitude of area
• Low latitudes – normal cylindrical
• Middle latitudes – conical projection
• High latitudes – normal azimuthal
– Extent
• Broad E-W area (e.g. US) – conical
• Broad N-S area (e.g. S. America) – transverse cylindrical
– Theme
• e.g. Equal area vs. conformal (scale same in all directions)
From M. Helper, University of Texas, 2008
How to know which map projection to
use?
• General guide:
http://erg.usgs.gov/isb/pubs/MapProjections/
projections.html
• Conventions for different areas or fields of
study
Overall View of GIS
Key Questions and Issues
•
•
•
•
What is GIS?
What are the applications of GIS?
How is the real world represented in GIS?
What analyses can GIS perform?
What does GIS stand for?
• GIS is an acronym for “Geographic Information
System”
What is GIS?
• Computerized management and analysis of
geographic information
• Group of tools (and people) for collection,
management, storage, analysis, display and
distribution of spatial data and information
• Computer-based tool for mapping and
analyzing things that exist and events that
happen
• Refer to readings for other definitions
From M. Helper, University of Texas, 2008
GIS Software
• There are several GIS software programs available for
use.
– Open source (not necessarily free)
•
•
•
•
MapServer
TerraView
Quantum GIS
UDig
– Proprietary software
•
•
•
•
•
IDRISI
GMT
Manifold
MapPoint
ESRI (used in class)
GIS Example
From M. Helper, University of Texas, 2008
A GIS is Composed of Layers
Geology
DEM
Digital
elevation
model
Hydrography
Roads
From M. Helper, University of Texas, 2008
Features have locations
Stavanger
X = 638539 m
Y = 8135093 m
X axis
Y axis
Origin (0, 0)
From M. Helper, University of Texas, 2008
Spatial relationships can be queried
• What crosses what?
• Proximity – What is within a certain
distance of what?
• Containment - What’s inside of
what?
• Which features share common
attributes?
• Many others
From M. Helper, University of Texas, 2008
Remember
• GIS focuses on geographic information
• If something has a location or is associated
with a location, it can be mapped.
Key Questions and Issues
•
•
•
•
What is GIS?
What are the applications of GIS?
How is the real world represented in GIS?
What analyses can GIS perform?
The Global Positioning System
From M. Helper, University of Texas, 2008
GPS Facts of Note
• USA Department of Defense navigation system
– First launch on 22 Feb 1978
– Originally 24 satellites
• Today ~30 satellites for GPS
From M. Helper, University of Texas, 2008
GPS Milestones
•
•
•
•
•
•
•
•
•
1978: First satellites launched
1983: GPS declassified
1989: First hand-held receiver
1991: S/A activated (large error in location)
1993: GPS constellation fully operational
1995-1996: First hand-held, “mapping-grade” receivers
1996-1998: GPS on a microchip
1997: First $100 hand-held receiver
2000: S/A off (more accuracy)
From M. Helper, University of Texas, 2008
GPS Segments
• Space – Satellites (SVs).
• Control – Ground stations track SV orbits and
monitor clocks, then update this info for each SV, to
be broadcast to users.
• User – GPS receivers convert SV signals into position,
velocity and time estimates.
From M. Helper, University of Texas, 2008
How are SV and receiver clocks
synchronized?
 Clock errors will cause
spheres of position (solid
lines) to miss intersecting
at a point.
 Adjust receiver clock
slightly forward will cause
larger DT(=larger sphere;
dashed) and intersection at
point.
 Requires 4 SVs, not 3
as shown, for clock error
& X, Y, Z
From M. Helper, University of Texas, 2008
Satellite Positioning
Observe DT
Determine
Orbit
Known
Geocenter
From M. Helper, University of Texas, 2008
3-D (X, Y, Z) One-way Ranging
• Intersection of 2 spheres of position yields circle
• Intersection of 3 spheres of position yields 2 points
of location
– One point is position, other is either in space or within
earth’s interior
– With earth ellipsoid (4th sphere)
• Get receiver clock synchronized and X & Y but no Z
• Intersection of 4 spheres of position yields XYZ and
clock synchronization
From M. Helper, University of Texas, 2008
Sources of Error
Satellite Orbit Errors (~2.5 m)
SV clock error (~1.5 m)
L2
L1
Ionospheric Refraction (~ 5 m)
(Can correct with L1 & L2 DTs)
50 km
Tropospheric Delay (~ 0.5 m)
200 km
Multipathing (~0.5 m)
+ GDOP (errors x 4-6)
(Geometric dilution of precision)
From M. Helper, University of Texas, 2008
Satellite Constellation
• Must have a good spread of satellites
• http://en.wikipedia.org/wiki/File:Constellation
GPS.gif
GPS Resolution and Map Scales
From M. Helper, University of Texas, 2008
Familiarization with GIS
Software used is ESRI ArcGIS, but
concepts are the same with any GIS
software program.
Vector data
Vector data
• An x, y coordinate system references the realworld location.
• Shapefiles and feature classes (file types) are
vector data.
• Appropriate for discrete data where
boundaries are needed.
– Pipeline location.
Raster data
Raster data
• Assign a value to a cell.
Raster data
• Raster data may be a georeferenced jpg or tiff,
or a converted ASCII grid.
• Appropriate for continuous data where
discrete boundaries are not necessary.
– Topography
• Grid files
– Cells contain Z data.
– The smaller a cell size, the higher the resolution.
Practical uses of raster data
• Simple display of a raster
– Topography (elevation)
– Bathymetry (depth)
– Gravity
– Magnetic anomalies
Advanced uses of raster data
• Additional processing of raster
– Changes in morphology
– Sediment thickness
– Hill shades (Creating texture)
– Contours
– Topographic profiles
– Spatial analysis
– Map algebra
Using Satellite Data with GIS
• GPS Data
– Datapoints
– Tracks
• Remote Sensing Data
– Satellite images
– RADAR
Beijing, China
http://www.globalsecurity.org
Oman
http://www.satimagingcorp.com
Using Satellite Data with GIS
– Digitize buildings and roads
– Digitize faults, scarps, rivers, or
elevation
Beijing, China
http://www.globalsecurity.org
Oman
http://www.satimagingcorp.com
Title bar
ArcMap document
Map area
Table of
contents
Coordinates
Acquiring External Data
• Government and non-government agencies may
provide free GIS data
• Quality
– Map purpose influences acceptable quality
General Websites: Shapefiles
• Norwegian Petroleum Directorate
www.npd.no
• GIS Data Depot
data.geocomm.com
• DIVA-GIS
www.diva-gis.org/gdata
• Norwegian Geological Survey (NGU)
www.ngu.no
• United States Geological Survey
www.usgs.gov
• Many others
General Websites: X,Y Data (Need
Converting)
• USGS NEIC Earthquake Database
http://neic.usgs.gov/neis/epic/epic.html
General Websites: Grids
(May Need Converting)
• General Bathymetric Chart of the Oceans (GEBCO)
www.gebco.net
• CGIAR-CSI SRTM
Processed NASA satellite topography data
http://srtm.csi.cgiar.org/
• Scripps Institution of Oceanography
http://topex.ucsd.edu/marine_topo/
• NGDC World Magnetic Anomaly Map
www.geomag.us/models/wdmam.html
General Websites: Maps
(Need georeferencing)
• The University of Texas at Austin PerryCastañeda Library Map Collection
www.lib.utexas.edu/maps/
• Google Image search
Identify features
• Select the identify tool.
• Click on a feature.
Why select features?
•
•
•
•
Create subsets
Find data
Find counts of data with certain attributes
Find data near a location
Select by attributes
• Use Select by Attributes
wizard
• Use when attribute
values are known and
assigned
• Can be unique
Select by location
• Use select by Location
wizard
• Location with buffers
– What is a buffer?
• Location with respect to
another dataset
Creating and editing shapefiles
• Not all data that is needed for a mapping
project will be available in GIS format
• Some data is extremely expensive to buy
• Some data is not available for purchase
• Sometimes the GIS technician needs to create
new data based on other map layers
Georeferencing
What is Georeferencing?
• It is a process by which locational information
(geo) is added (reference) to an image (raster)
in a GIS program.
• A point on the image is assigned a coordinate
pair in two ways:
– By lining up the image to a feature
– By adding coordinates directly
For Example:
• Align raster image to vector data (shapefile or feature)
Nature of the problem:
• Data source
registration may
differ by:
– Rotation
– Translation
– Distortion
Rotation
Differential Scaling
Translation
Skew
Distortion
From M. Helper, University of Texas, 2008
General problem is then:
Control Points
(0,1)
(1,1)
(501000, 3725000)
(0,0)
(1,0)
Source (x, y)
(“Warp”)
(498100, 3715000)
Destination (X’, Y’)
From M. Helper, University of Texas, 2008
What images to use?
• Trusted sources (published maps from map
agencies)
• Clear coordinate system markings (Decimal
degrees for Geographic Coordinate Systems;
Meters for UTM and Mercator, but need a
reasonable guess of UTM zone or Mercator)
• Clear country boundaries, city locations, major
roads, major rivers
What images to discard?
• Sketchy sources (personal websites or
unpublished sources)
• Blurry, coarse or very thick country
boundaries. These are usually overgeneralized.
• Maps that rely on other maps to show their
locations (over-use of inset maps)
• Exceptions: Very old maps which are not
available in an updated form!
Digitizing from Georeferenced Image
• Obtain information that has not been
published in GIS
• Obscure publication or out-of-print
publication
• Error margin depends on overall scale of data
(global vs continental vs regional vs
country/state vs town)
Practice: Good or Bad?
Practice: Good or Bad?

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