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GGR278 Lecture 10

GGR278 Lecture 10 Raw
GGR278 Lecture 10 Flashcards

• Completed Notes Status

  • Completed insertions: 1
  • Ambiguities left unresolved: none

• Lecture Summary

  • Central objective: To introduce and differentiate between local and focal raster operations in GIS, focusing on their mechanisms, statistical applications, and practical problem-solving capabilities.
  • Key concepts:
    • Local Raster Operations: Operations calculated on a per-cell basis, completely independent of neighbouring pixels. They can be performed on a single raster (e.g., Raster Reclassification, map algebra) or multiple rasters (e.g., local statistics, frequency, popularity, ranking, and position).
    • Raster Reclassification: A single-raster local operation used to convert known values into a new schema via data aggregation, range grading, or rescaling (normalization).
    • Focal Raster Operations: Neighbourhood-based operations where a cell's output value is determined by the values of its surrounding cells (e.g., smoothing, edge detection, slope calculation).
  • Connections:
    • Local Raster Operations and Focal Raster Operations are foundational spatial analysis tools. While local operations are isolated to matching pixel coordinates across layers, focal operations introduce spatial context by evaluating adjacent cells (neighbourhoods), which introduces complexities like edge cases and missing data handling.

• Practice Questions

  • Remember/Understand:
    • What is the fundamental difference between a local raster operation and a focal raster operation?
    • How does the "Variety" statistic function in a multiple-raster local operation?
    • What does "Local Position" return when analyzing multiple overlapping rasters?
  • Apply/Analyze:
    • If you have 10 years of annual precipitation rasters, what sequence of local operations would you use to determine how many years had precipitation above the 10-year average?
    • Why might you choose to invalidate an entire focal region if it contains a single "no data" point, rather than ignoring the missing data?
  • Evaluate/Create:
    • Design a workflow using local ranking and local position to identify not just the highest temperature month for a given region, but the second and third highest, explaining how ties would be handled.

• Challenging Concepts

  • Local Raster Operations:
    • Why it's challenging: Differentiating between closely related multiple-raster operations like Local Popularity, Local Ranking, and Local Position can be confusing.
    • Study strategy: Memorize the specific output of each: Popularity outputs the value that appears most often, Ranking orders the values and picks a specific index, and Position outputs the layer number (raster input number) that meets a condition (e.g., highest value).
  • Focal Raster Operations:
    • Why it's challenging: Handling edge cases and missing data requires understanding how the "neighbourhood" shape (circle vs. square) interacts with the spatial extent boundary.
    • Study strategy: Draw a 3x3 grid on paper, place it on the edge of a larger grid, and physically count the "non-existent" cells to visualize why spatial extent boundaries skew focal calculations.

• Action Plan

  • Immediate review actions:
    • Review all [COMPLETED] insertions and verify with course materials
    • Re-read Lecture Summary and confirm key links
  • Practice and application:
    • Answer Remember/Understand questions
    • Answer Apply/Analyze questions
    • Attempt Evaluate/Create questions
    • Review the GGR278 Lecture 10 Worksheet to ensure the practical application of precipitation data is fully understood.
  • Deep dive study:
    • Focus on Challenging Concepts (above)
    • Extend atomic notes only where the new lecture adds content
  • Verification and integration:
    • Cross-reference notes with textbook/slides
    • Identify remaining gaps
    • Link this lecture to prior/future lecture notes (lecture notes only; no MOCs)