GIS for Environmental Studies: Lecture 2

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GIS for Environmental Studies Lecture 2

• Today we will cover
• More on ArcMap
• Map scale
• The type of data you can use to make a map
• GPS
• Your group mapping project (and hopefully will
  have time to get into project groups)

Please note that portions of the material in this
lecture come from Maribeth Price, author of your
text.
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Menu bar
Map scale
Toolbars
Map window in Layout View
Table of Contents
Data frames
Active frame
View Mode
Map units display
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The table of contents
Place layers in data frames
Change draw order
Access layer properties
Turn layers on/off
Change symbol properties
Draw Order
Display or Source mode
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What is a layer?

• Spatial data file
• Associated properties
• Held in memory in ArcMap
• Used as inputs to functions/tools
• May be saved as a file

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Layers for display
Same shapefile Different symbols
Two layers, one shapefile
C\workshop\mgisdata\sturgis\stands2.shp
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Layers for copying symbols
--layer file
Store symbols, labels, and display settings for
single or groups of feature classes and open them
in new map documents quickly.
One-click
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Layer Properties
Properties tabs
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View Mode
Refresh
Data view
Layout view
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Map scale

• Ratio of distance on the map to distance on the
  ground
• Dimensionless cm or inches or mm

1 cm on map 100,000 cm on ground
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Talking about map scale

• A large denominator gives a small fraction ? a
  small scale map. It shows a large area.
• A small denominator gives a larger fraction ? a
  large scale map. It shows a small area.

1 -------- 50,000,000
1 -------- 500,000
1 -------- 5,000
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Digital vs original scale

• Once in GIS data may be displayed at any scale,
  BUT
• Original scale of the map does impact the
  precision and accuracy of the data.

Original scale 1100,000
Original scale 110 million
You should not display or analyze data at scales
very different from the original source data.
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Units

• The cursor position on the screen may be read in
  several different types of units.
• Map units are determined by the x-y coordinates
  stored in the data file.
• Usually they are in degrees, feet, or meters
• Display units can be set by the user, so that the
  coordinates may be viewed in any desired unit,
  such as miles.
• Page units show the location on the map page
  layout, usually in inches or cm.

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Pop-quiz (look at previous slide)

• Is this in data view or layout view?
• How many layers do you see?
• Which layer is currently on?
• If we clicked on all the layers, which would be
  draw on top?
• What are the display units in?
• What is the map scale?
• Would you call this a large or small scale map?

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Where do we get data from? 1. Existing data
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2a. New sources Aerial photography

• Photo can be scanned in and used as a raster
  image for further processing or used as a
  background (Atlanta example)
• Digitizing (use a device that allows you to hand
  trace maps OR trace maps on your computer screen
  using a mouse).

New Orleans, after Katrina
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2b. Satellite Data
Nebraska. Landsat Thematic Mapper by assigning
bands 7, 4 and 3 to red, green, and blue
respectively based on moisture crop calendar.
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2c. GPS
Cabbage Palms

• Use GPS points as a point cover.
• Use GPS points a guides to draw in polygons of
  buildings, etc.

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What is GPS?

• a satellite based method of determining
  geographic positions
• Developed by the US Military
• Previous methods (e.g., Loran) used towers for
  navigation

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Satellite information

• High orbit so we can access them without
  interference
• 12hr. Orbit
• 24 satellites

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How does GPS work?  Triangulation 1 satellite
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  Triangulation-2 satellites
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 Triangulation-3 satellites
4th satellite makes it more precise
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How does your GPS unit know how far away the
satellite is?

• 2. GPS measures the distance using the speed of
  light
• 3. GPS and satellites have atomic (near perfect)
  clocks

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• Satellite knows its exact position
• Any corrections due to atmosphere or other
  factors can be made

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How accurate is GPS?

• lt1cm 70m off, depending on receiver,
  differential correction, luck
• Main Sources of Error
• 1. Atmospheric Error (30m)
• 2. Geometric Dilution of Precision (10m)
• 3. Multipath Errors (1m)

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Atmospheric errors
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Geometric Dilution of Precision(GDOP)
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Multipath Errors
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Increasing accuracy differential correction
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Your mapping project

• You will be placed in a group of 3. Your group
  must decide to collect point data on anything on
  campus. Caveats
• Must not need high accuracy
• Must generate enough work for 4 class periods
• You will be making maps using the data for
  Project 5

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Some ideas for projects

• Map of the location of several species of wading
  birds (record behavior, habitat)
• Map the location of ibis groups (record group
  size, habitat)
• Map the location of rabbit pellets (record of
  pellets, habitat)
• Map unusual trees on campus (record species, dbh)
• Map locations of Brazilian peppers in the palm
  hammock or on campus in general (record dbh, if
  it has berries)
• Map the location of yellow bikes (record serial
  number, condition)

Youll learn how to use a GPS unit on this Friday
or next.
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Data entry
Brazilian pepper trees

• Enter data into excel within 3 days of
  collection. You might want to rotate the duty
  or split it up. (e-mail the data to the group)
• Put latitude in one column, longitude in another.
  Attributes can be in the following columns.
• BE ACCURATE

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Your idea

• Now youll meet with your group come up with a
  mapping project
• On a piece of paper, list your group members and
  briefly describe your project
• Each group will be given a simple GPS to use
  during class time.
• Let me know if you have any additional equipment
  needs.