Area

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Chapter 5
Measurements

• Chapter 5
• Area
• Perimeter
• Buffer
• Group

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Modules used in measurement?

• Area
• Perimeter
• Distance
• Buffers
• Group

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Area Gray 15
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Modules used in measurement?

• Area
• Perimeter
• Distance
• Buffers
• Group

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Area Gray 15 Orange 10
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Modules used in measurement?

• Area
• Perimeter
• Distance
• Buffers
• Group

Count em
Area Gray 15 Orange 10
Perimeter Gray 30 Orange 28
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Area and Perimeter Outputs

• An image or map where each region is given the
  attribute of area
• On screen tabular summary that lists each
  attribute and it area (in area units)
• Values file containing integer attributes and
  their areas
• If the soils data defines the regions of interest
  then .

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Looks like the soils image!
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And as a Values file
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Contiguous?

• What does the word mean?
• Abutting
• OK, by how much?

Idrisi has two case for contiguous cells the
cells abut on sides the cells touch at the
corners
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Grouping

• There are 4 orange areas and 3 gray areas.
• So if I want the areas of these regions, made up
  of contiguous cells, I have a problem.
• GROUP to the rescue!

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GROUP
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• Using Group I can make a new image which has a
  new attribute for each of the regions - a group
• GROUP scans the image and assigns group
  starting in upper left

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Area of 1 10, of 21, of 34, of 41, of 64,
of 71
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Diagonal linked groups
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• How many groups if I use diagonal linking?
• ______?

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Distance

• The distance function is available in most raster
  GISs because it is basic to other operations
• A distance image starts with an image which
  contains non-zero source or target pixels.
• DISTANCE calculates the minimum distance between
  each non-source cell and it nearest source.

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Computing Distance
Source
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Distance from Lake

• Distance from Lake Nifkin

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Buffers

• Are Boolean (1 or 0) images which define are area
  that is within a given distance of a target or
  source set of pixels or cells.
• The source is a set of non-zero pixels in an
  image where all the other cells are 0.
• The source set can be
• A single pixel
• A line of pixels (as from a road or stream)
• An area (as from a lake)
• Buffers can be made by
• Computing distance and reclassing
• Using the Buffer command

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Reclass to make buffer

• Reclass distance so that lake 0
• Buffer 1
• Outside buffer 0

1001
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Buffer around lake
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An Application
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Example from book
This is a logical OR
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Grouping Example (Book)

• Start with cover type

Now we have identified 4 areas of wetland that
are NOT connected at corners but have lost what
kind of wetlands they are
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Grouping Example (Book)
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Grouping Example (Book)
Now that we have found the wetlands larger than 5
pixels we need to know what kinds of wetlands
these are.
X

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Spatial Model

• Webpage
• What is it?
• Real life process simplified
• Why bother?
• Plan on how youll get there (a DRAFT model)
• Keep track of where you have been
• Keep track of what works what does not
• Explain how you got an answer
• the parts that are important
• Communicate what you did

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With all measurements

• CELL size and shape are important
• Distance unit important
• 165 165 27,225 sq.ft. area
• 27,227 ft2 0.6257 Acres
• 165 4 660 perimeter

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Map Composition

• Title
• Legend
• Scale
• North Arrow
• Credits
• Borders
• Symbolization
• Balance