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
Digital Map in cyber space
In addition to traditional static mapping, more and more online mapping features are available. For example: Street views (Bing Maps, Google Maps), Draggable driving directions, Birds Eye View (Oblique photographs) etc.
Street Views
Street view car, snowmobile, trike, Grand Canyon Trekker
Augmented-Reality Maps
Augmented Reality GIS Maps (2007), TED Presentation (2010), Google Eyes (2012)
Map Compositions
Map body, title, legend, scale, direction indicator, map metadata, inset/ overview map
Direction Indicator - Grids
A grid is a network of parallel and perpendicular lines superimposed on a map.
Direction Indicator - Graticules
Graticule is a network of longitude and latitude lines on a map that relates points on a map to their true locations on the Earth.
Inset Map
Shows more detailed area and additional maps that map body didn’t display.
Overview Map
Used to identify the map body’s general location in a coarser scale
Geovisualization - 3D visualization
- Easier to interpret data - for common publics
- Demonstrate your proposals in a more natural and direct approach - for both specialists and general publics
- Visualize data in 3D to identify patterns not apparent in 2D (Volume of reservoir, visibility analysis)
Geovisualization - Geographic Visualization
- The creation and use of visual representations to facilitate THINKING, UNDERSTANDING, AND KNOWLEDGE CONSTRUCTION about human and physical environments, at geographical scales of measurement.
- Geovisualization is used to explore, analyze, synthesize, and present spatial data.
- Increase the interactions between users and digital maps - VGI and PPGIS
- Improve the Virtual Reality (VR)
Augmented Reality Map/ Geovisualization for Forestry/ Virtual Reality/ 3D CitiesEngine
3D appearance/ UGA Project/ Cityscapes in 3D
Digital Elevation Model (DEM)
DEM is the digital cartographic representation of the elevation of the terrain at regularly spaced intervals in x and y directions using z-values referenced to a common vertical datum (USGS)
- Elevation, Slope, Hillshade, Contour, Aspect, Viewshed
DEM v DTM (T = Terrain)
- DEM (DSM)s - measure the terrain elevations for ground positions at regularly spaced horizontal intervals (in addition, DEMs include BUILDINGS, TREES and ANY OTHER OBJECTS OVER THE EARTH’S SURFACE)
- A Digital Terrain Model (DTM) measures the heigh of the earth’s surface ONLY.
Metadata
“data about data”
What we look at to find many things, such as where our data was collected, its extent, the units, and others
On-the-Fly
This means ArcMap can display data stored in one projection as if it were in another projection
