Lecture 4 (Generalization and Geovisualization) Flashcards
Why Generalization?
“You are here!” TOO MANY DETAILS/ TOO FEW DETAILS/ Finally! Just the right amount of information
Can a map be perfect?
- The real world is infinitely complex
- A map must always approximate, GENERALIZE, abstract, or simplify
- Simple and quick answer: No!
Implement Generalization
- Two fundamental types of geographic phenomena
- Generalization for DISCRETE OBJECTS is easy to understand: POLYGON can be generalized (simplified) to a POINT
- But, how to generalize CONTINUOUS FIELDS?
Generalization of Continuous Fields
- Many geographic phenomena are conceptualized as fields (exactly one value of the phenomenon exists at every point on the Earth surface - e.g. elevation and precipitation)
- In principle, a field can take a different value everywhere (An infinite amount of info, Tobler’s Law helps by virtually guaranteeing that variation will be smooth and slow over space)
Six Ways of Representing a Field (See Printed Paper)
a) regularly spaced sample points
b) irregularly spaced sample points
c) rectangular cells
d) irregularly shaped polygons
e) irregular network of triangles
f) polylines represent countours
Map generalization
- Reduces complexity from the real world
- Retains spatial and attribute accuracy (at the specified scale level)
- Accounts for map purpose and scale
- Provides more useful ‘information’ or more efficient communication and presentation
Methods of generalization
McMaster and Shea (1992) identified 10 distinct types of generalization rules.
10 distinct types of generalization
Simplification, Smoothing, Collapse, Aggregation, Amalgamation, Merging, Refinement, Exaggeration, Enhancement, Displacement
Object Types in Vector Format
From (Point, Node to Vertex, Arc/ i.e., Line To Node) Point Feature
Simplification
Weeding - Remove points in the outline of a polygon to create a SIMPLER SHAPE.
Smoothing
Replace the SHARP and COMPLEX parts and make the result LOOK SMOOTHER
Collapse
Replace an area object by a COMBINATION OF POINT AND LINE OBJECTS
Aggregation
Replace a large number of distinct symbolized objects by a smaller number of new symbols
Amalgamation
Replace several area objects by a SINGLE AREA OBJECT
Merging - common form of generalization
Replace several line objects by A SMALLER NUMBER OF LINE OBJECTS from their most similar neighbors.
Refinement
Replace a complex pattern of objects by a selection ones, and preserves THE PATTERN’s GENERAL FORM
Exaggeration
Relatively enlarge an object to PRESERVE ITS CHARACTERISTICS when changing the map scale.
Enhancement
Emphasize THE PHYSICAL SIZES OR SHAPES of symbols, and preserve the PATTERN’s GENERAL FORM.
Displacement
Move THE OBJECTS FROM THEIR TRUE POSITIONS, but still preserve their visibility and distinctiveness.
Map Generalization
Simplifies the complexity and provides us the clear, useful and correct information
How to design a map?
Inset map, Map Body, Scale, Legend, Title, North Arrow, Projection, Data Source, Author
GOAL of Map Design
Primary Goal - Share information - Highlight patterns and processes - Illustrate results Secondary Objective - attracting our audiences PROVIDE A GOOD-LOOKING, SIMPLE, AND ELEGANT MAP TO MEET ITS PURPOSE
Principles of Map Design
Purpose - one or multiple, what/ how to display
Reality - reduce the complexity in map
Available data - raster or vector
Map scale - quality of map, level of detail
Audience - different backgrounds/ expectations
Conditions of use - where to use it
Technical limits - digital map or hard copy
Digital Map v Paper Map (See Printed Sheet)
GIS is a flexible medium for the production of many types of maps
