2'2'1, 2'3 skip 2'3'4, 2'4, 2'5, 2'6

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Chapter 2

• 2.2.1, 2.3 (skip 2.3.4), 2.4, 2.5, 2.6

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Map Typemany, be sure to fit the type to the
data and the spatial questions
Color/shading to represent categories
Feature location
Dot number to reflect quantities
Lines of equal value
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Now to mess with your head.
Common Mistake Large Scale vs. Large Area People
are often saying "large scale" map when they mean
"large area". A large scale map is one where
the fraction is large.
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Map Scale
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Georeferencing Features on the Earth

• Requires a reference system (coordinate system)
• Hence requires a means of representing the
  surface accurately
• 3. Ultimately need to represent this 3d reality
  in 2d (screen or paper)

Then we can worry about GIS data and spatial
questions
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Spherical Coordinate System
(Geographic in Arc and other places)
1. Applies a cartesian (X,Y) to a globe using the
poles, equator and prime meridian as references
Produces the familiar Latitude, Longitude (i.e.
deg, min, sec) with values calculated from the
horizontal angles above/below equator or E, W of
meridian
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Challenges
1. The earth is not a sphere
2. A global (spherical) system is not necessarily
the most accurate at a specific location or often
is not as mathematically convenient for
conversions/transformations to other system.
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Ellipsoidbetter represents the general shape of
the earth.
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Geoidmathematical (measured) reference
surface---average sea level
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When combined the ellipsoid allows more accurate
horizontal (x,y) location while the Geoid
provides a reference for elevation (z)
valuesmore accurate than spherical, more
mathematically convenient than reality.
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However.
Increased accuracy and precision means that no
single model will work for the entire planetmost
important in representing 3d as 2d.
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Datum
A reference surface (including the geoid and
ellipsoid) but often is a more regional measured
surface used as the basis for spatial measurements
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Survey Network, 1981
(from Schwartz, 1989)
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Get to the point!!!!!!!!!!!!!!!!
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Ultimately we need to project our 3d
information to a 2d surface for display, analysis
etc.
Information you need to quantify your location
(x, y, z) and calculate spatial attributes like
length, area, perimeter volume comes directly
from the system used to represent the earth and
to locate you on it.
The method used to project the spatial
information onto a 2d surface will determine the
spatial units as well as the ability to overlay
other layers.
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No matter what system is used some sacrifices
are made. Area, Shape, Distance, Directionat
least 1 will be sacrificed in projecting from 3d
to 2d.
transformation
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Map Projections
A mathematical way of placing 3d features onto a
2 d surface.
Not unlike projecting a photo onto a flat screen
The nature of the projection needs to fit the
location
Many global, regional and local projection systems
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The point When you use, collect, create,
modify, project GIS data layers you NEED to pay
attention to the projection system
used. Incorrect projection information can
result in. Layers wont match---cant overlay
or analyze. Spatial measurements can be
wrong---differences can be subtle Arc will not
let you run some analysis or other tools w/
mismatched projections. NOTE Arc will project
on the fly wherever it can so even layers w/ a
different system will sometimes match in the
data window.
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Projection systems commonly used in GIS
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Universal Transverse Mercator UTM System
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UTM Zone Details
Each Zone is 6 degrees wide Zone location
defined by a central meridian Origin at the
Equator, 500,000m west of the zone central
Meridian Coordinates are always
positive Coordinates discontinuous across zone
boundaries
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UTM Zones
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State Plane Coordinate System Zones
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State Plane Coordinate System

• Each state partitioned into zones
• Each zone has a different projection specified

California State Plane Zones
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GIS Data and Data Collection(2.6) 4 basic options
1. Field data collectionland survey, GPS etc.
2. Extraction from aerial or satellite imagery
3. Use existing data(NOTE you will have less
control over collection, compilation, accuracy
etc.). You will use A LOT of this type of data
just be aware of the potential limits.
4. Combine field data w/ imagery or existing
data. Allows you to assess accuracy.
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GIS Data Formats, Management, and Attributes
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Vectors Points, Lines, Polygons
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Fields can be nominal, ordinal or interval/ratio
and may or may not be spatial
Additional fields can be added and calculated
Tables with identical fields can be joined
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Vectors Points, Lines, Polygons
Generally 1 row/feature
Can be many (i.e. 1 row/line segment
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1 row per pixel value usually
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Aerial and Satellite Images in GIS (Chapter 6)
I. Remote Sensingessential source of much of the
data used in GIS

• Basic Principles

1. Reflected and emitted radiation sensors
passive

• Sensors gather light reflected from Earths
  surface
• Visible and IR wavelengths are common but also
  thermal IR

2. Active systems bounce a signal off the
Earth and collect energy returned
a. Radar, Lidar
b. Active systems can be used in cloudy or
nighttime situations
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3. Understanding what you see on the screen
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Image Formats
1. Single band (1 layer) light is collected
from just 1 region of the spectrum
2. Multi-band (multispectral)--light is
collected by a sensor from usually 3 or more
regions of the spectrum
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When we display color images we use combinations
of red, green and blue to generate the colors.
We can display any 1 level or Band of an image
alone as well
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Bands are selections from specific regions of
the EMS. By studying the ways in which light
energy from these bands interacts with Earth
features we can develop maps, and models to
characterize the Earths surface.
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Spectral Signatureswhat informs us about
features represented in an image
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Near Infrared
Green
Red
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Raster or Grid
Remember Each cell gets 1 value/band
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Unlike traditional photographs, digital images
are numeric
Band 1 Band 2 Band 3
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Each pixel is assigned a number for each band
Values range from 0 (black) to 255 (white)
The numbers in each band give us clues as to what
the pixels represent
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Things to be aware of when working with remote
sensing imagery or air photos
Data needed or available Satellite image,
airborne sensor, air photo
Spatial resolution pixel size
Spectral composition Which bands are
available/used
Cloud cover, distortion, other error sources
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Uses of Aerial Photos

• Mapping and surveyinghigh resolution photos
  offer rapid ways to map features on the
  groundbest if combined with ground data

2. Form the base of many landcover maps (Lab
today)
3. Used to support other types of remote
sensing/GIS worki.e. photos can be used as a
source of ground truth in satellite image
classifications.
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Limits to the use of aerial images
1. Photos do not provide an orthographic view of
features.
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2. Other error sourcescamera tilt, atmospheric
interference, terrain differences, system
problems (i.e.lens/camera distortion)
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Locating a single point on the Earth. What
information is needed?
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Differential Correction (for various sources of
inaccuracy).
Requires a base station and GPS unit capable of
communication w/it.
Base station is known very accurately.
Differences between known location and that
estimated by the satellites on a give date will
be used to adjust GPS points.
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Base Station (est)
Measured GPS location
Base Station (known)
Adjusted w/ differential correction
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