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GGR278 Lecture 11

GGR278 Lecture 11 Raw
GGR278 Lecture 11 Flashcards

• Completed Notes Status

  • Completed insertions: 2
  • Ambiguities left unresolved: 1

• Lecture Summary

  • Central objective: Understand advanced raster operations (zonal and global) and evaluate different raster tessellation geometries.
  • Key concepts:
    • Zonal raster operation: Computes values based on defined zones (contiguous like watersheds, or noncontiguous like land use) rather than fixed geometric neighbourhoods.
    • Global raster operation: Computes values for a cell based on all other cells in the input raster, commonly used for Euclidean distance and cost distance.
    • Raster tessellation: The process of covering a plane with a grid of polygons (squares, hexagons, or triangles) without gaps.
    • Hexagonal vs. Square Grids: Hexagons offer better perimeter-to-area ratios, unambiguous connectivity, and better edge representation, whereas squares are superior for storage simplicity and resampling scalability.
  • Connections:
    • Builds on focal and local operations by expanding the spatial scale of computation (zones and global extents) and examines how the underlying geometry (tessellation) impacts spatial analysis and Relational database storage.

• TK Resolutions

  • #tk: idk (regarding Euclidean distance)
    • Answer: Euclidean distance calculates the absolute straight-line distance from the centre of each cell to the nearest source point.
  • #tk: One more part (regarding tessellation transformations)
    • If not answerable: The notes mention translation and glide reflection. The missing third mathematical transformation for regular tessellation is highly likely "Rotation" (where shapes connect seamlessly when rotated), but this must be verified against the lecture slides.

• Practice Questions

  • Remember/Understand:
    • What is the difference between a contiguous and a noncontiguous zone in a zonal raster operation?
    • Which three polygon shapes can be used to create a regular raster tessellation without gaps?
    • How does the storage requirement of a square grid differ from a hexagonal grid?
  • Apply/Analyze:
    • Why is nearest neighbour connectivity considered ambiguous in a square grid but unambiguous in a hexagonal grid?
    • If you are modeling wildlife movement and want to minimize edge artifacts, which tessellation shape should you choose and why?
  • Evaluate/Create:
    • Evaluate the trade-offs between using square grids versus hexagonal grids when a project requires frequent resampling to different resolutions.

• Challenging Concepts

  • Raster tessellation connectivity (Rook vs. Queen case):
    • Why it's challenging: Understanding why diagonal movement in a square grid distorts distance calculations (the Pythagorean edge issue).
    • Study strategy: Draw a 3x3 square grid and calculate the distance from the centre cell to an adjacent cell versus a diagonal cell to visualize the ambiguity.
  • Global raster operation (Cost Distance):
    • Why it's challenging: Differentiating between simple Euclidean distance and weighted cost distance matrices.
    • Study strategy: Review examples of friction surfaces (e.g., speed limits, terrain slope) and how they alter the "shortest path" compared to a straight line.

• Action Plan

  • Immediate review actions:
    • Review all [COMPLETED] insertions and verify with course materials
    • Address the [AMBIGUOUS] tessellation transformation item by checking the slide deck
    • Re-read Lecture Summary and confirm key links
  • Practice and application:
    • Answer Remember/Understand questions
    • Answer Apply/Analyze questions
    • Attempt Evaluate/Create questions
  • 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)