Abbey S- Week 3

Chapter 5: Finding What’s Inside

You can map what’s going on inside an area if you want to compare different areas or if you want to show what locations need action

• What’s inside a single area vs multiple areas
• Features either discrete or continuous

GIS can be used to:

• Figure out whether a feature is inside of an area
• Find all features in an area
• Find number of features in an area

Some features may be partially in an area

• Only use portion actually in the area

Three (3) ways to find what’s inside:

1. Draw features/ areas
   1. Effective visual 
   2. Need dataset of area boundaries and dataset with features
2. Selecting features within an area
   1. You determine the area/ layer, and GIS selects all features 
   2. Good summary of features in an area
   3. Cannot use for surfaces
3. Overlaying areas and features
   1. Good for finding which features are in a number of areas
   2. Requires more processing

Based on the information provided in the book, it seems like the second method is not particularly effective. It cannot be used for surface features and overlaying features (method 3) allows you to see the same information. 

More details on each method:

Drawing areas/ features

• Make sure it is easy to see what features are in the area
• Locations and lines require different symbols/ thicknesses in order to differentiate them from each other
• To map discrete areas:
  • Lightly shade the area
  • Make the area translucent or shade the area with a pattern
  • Draw only the boundary of the area
• To map continuous data:
  • Same as discrete
  • Place a screen on the outside area to emphasize what’s in the area

Selecting features in an area

• You determine the features and area, and GIS will let you know what features are within the boundaries of an area
• GIS does not distinguish which areas the features are in (L)
• You can use this method to generate a report of the results, which can be used to relay information to the masses

Overlaying areas with continuous categories/ classes 

• GIS uses vector/ raster method to overlay info
• Overlaying areas on areas requires slivers
  • Slivers are small areas that are slightly offset
  • An area with an areal extent less than the smallest dataset
• Raster vs vector
  • Vector- more precise but more processing
  • Raster- more efficient, prevents slivers, but sometimes less accurate

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Chapter 6: Finding What’s Nearby

What’s occurring around a feature?

• Important for projects that need to be conscious of the surrounding area (development, demolition, etc.)
• Measure line distance, distance/ cost over a network, or cost over a surface

Taking the curvature of the earth into account

• Planar method is used for smaller areas such as cities, states, or countries 
• Geodesic method good for regions and continents
  • Will be displayed with the curvature of the globe

Information from analysis 

• List
• Count 
  • By total 
  • By category
• Summary statistic
  • Total amount
  • Amount by category
• Statistical summary
  • Average
  • Minimum/ maximum
  • Standard deviation

Number of ranges

• Inclusive rings- how total amount increases as distance decreases
• Distinct bands- compare distance to other characteristics

Straight line distance:

• Defines area of influence around an area
• Quick ‘n easy
• Only gives an approximation
• Create buffer to define a boundary
• Select features in order to find features in a given distance 
• Calculate feature-feature distance to assign distance to locations
• Create distance surface to find continuous distance from source

Distance/ cost over a network:

• Measures travel over a fixed infrastructure
• More precise 
• Needs an accurate network layer
• GIS identifies all lines in a network
• Source locations in networks are centers
• Street neworks 
  • Street segments (edges)
  • Intersections (junctions)
  • Tagged with cost to travel from center to surrounding locations (impedance value)
  • Set travel parameters
    • Can specify cost for turns from one segment to another
• More than one center
  • GIS assigns segment to each concurrently

Cost over a surface:

• How much area is within an overland travel range
• Allows you to combine multiple layers
• Needs data preparation
• Creating a cost layer
  • The book uses an example of the cost between deer traveling through open forest vs thick underbrush, and how it would be easier for deer to travel through open forest (yay animals). Therefore, open forest= lower cost
  • Reclassify layer based on existing attribute

For me, this chapter really showed how specific you can get with GIS, especially when it came to determining traveling costs over a network or surface!

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Chapter 7: Mapping Change

Mapping change allows us to make predictions on what the future could look like (big emphasis on meteorology) 

Types of change:

• Location
  • How features will move
  • Can map features that physically move or geographic phenomena that change locations
  • Discrete features can be tracked as they move through space (organisms or meteorological events)
  • Events happen at different locations (earthquakes, deaths)
  • Showing patterns of movement for individual features or
  • Number of large yet distinct features 

• Character/ magnitude
  • How conditions in a given place have changed
  • Discrete features are changes throughout a period of time
  • Data summarized by area are presented as percentages or totals
  • Continuous categories show the type of features in a place
  • Continuous values are quantities that fluctuate
  • Magnitude- similar issues as mapping most and least (ch. 3)
  • Character- the way categories are defined may differ between dates

Measuring time:

• Three types of patterns
  • Trend- change between two periods
    • Increasing or decreasing?
  • Before/ after- self explanatory
    • Impact?
  • Cycle- change during recurring time period
    • Patterns?
• Choosing time interval
  • Need to choose interval if given a range 
  • Should be long enough to show change, but include all info
• Three ways to map change
  • Time series- change in boundaries, discrete areas, surfaces
    • Good visual impact, easy to understand 
    • Need comparisons
  • Tracking map
    • Showing movement of discrete locations, linear features, area boundaries
    • Easier to see subtle movement compared to time series
    • The more features, the harder to read
  • Measuring change
    • Show amount, percentage, rate of change
    • Shows difference in values
    • Omits actual conditions

Number of maps to show

• Fewer maps spaced longer apart shows more drastic change
• More maps account for possible patterns that may have been missed
  • More maps are more overwhelming for the viewer

Results

• Showing tables and graphs can supplement what you are trying to show thru maps

Mapping linear features

• Differentiate between each point with labels, colors, or symbols

Mapping contiguous features 

• Draw boundaries for areas at each date/ time

Mapping events

• Use different colors for each time period