Buffers: distance transformations make more maps

Objectives of Lecture:

1. Reminder of coming events (next week: Discussion 2 (Case Study))
2. Looking ahead to Winter Quarter: Geog 461 and 458
3. Prepare for Exercise 4 (DON'T panic! Not until 3/4 November)
4. Explain buffer construction for raster and vector
5. Distance measurements

In either case, the edge of objects form the basis for sending a contour outwards or inwards.
A fixed distance is used in place of a more careful study of the actual hazard/risk. [See an example about a series of studies in Illinois locating landfills]

Example: Timber, Fish Wildlife Agreement, Washington State

Riparian Management Zone (RMZ) Requirements

Water Type & Width    Maximum RMZ Width
Class 1&2  >75'            100'
Class 1&2 <75'              75'
Class 3 > 5'                50'
Class 3 < 5'                25'

Note: a minimum width of buffers is set to 25' for all water types and widths. Classes of water are defined in WAC 222-16-030. Source: WAC 222-30-020 (4c)

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Construction of Buffers:

Vector: fixed distances create contours (isolines of equal distance) gives a precise location for a specific regulation, gives zones between...
Each segment throws out a zone around it (two half circles and one rectangle).
To generate a buffer, construct these objects around each segment, overlay all the objects, aggregate to remove duplicate areas.
See Figure.

Raster:

measures distance to center of each cell, comes in steps of cell width

Each cell is exactly one cell width away, shorter distances cannot be detected (resolved). Diagonals can be estimated from Pythagorean theorem, see Figure.

Results of a distance measurement

• Amazon project in Oceanography UW : Distance from mouth of Amazon;
• Wilderness Quality Mapping (Arctic Scandinavia)
• Are you closer to a wetland or a road? (subtract the two distance surfaces)

Class participation in distance measurement

Post-It Notes, parallel 'computer' simulation

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Voronoi zones around points

Voronoi network (dark thinner lines) divides the region into areas closer to a particular point than any other (formed by pendendicular bisectors of lines between neighboring points).
Example: Amazon basin used for classic purpose to estimate rainfall input from weather stations
The Delaunay trinagulation (thicker grey lines) is the network of the connections between points that have a nearest neighbor relationship.

Beyond Voronoi: "Extended" neighborhoods for non-point objects (lines forming polygons)