Representations / Models

1
Representations / Models
2
Why Representations or Models?

• How do we know what we know?
• Human sight
• Visible spectrum, horizon at 10km visibility 100
  km
• Human sound
• 50Hz to 15KHz up to 100 m
• Taste, Touch, Smell

3
Surface of the Earth?

• 500,000,000 sq km
• on average 100 sq m is sensed directly
• p 100/500,000,000,000,000 m
• p 0.0000000000002 or 2 x 10 -13 spatially
• 5 billion years
• we live through 70
• p 70/5,000,000,000
• p 0.000000014 or 1.4 x 10 -8 temporally
• \ we know almost nothing of the surface of the
  Earth via our senses!

4
Knowing the World

• Everything else via communication
• Speech
• Text
• Photographs
• Radio, TV
• Maps
• Internet
• Databases

5
Jonathan Rapers Week in 2-D
1km
Each color 1 day
Darker later in the day
Courtesy Jonathan Raper of City University
London, GISci 2002 Keynote
6
Jonathan Rapers Month in 3-D
X y axes are spatial and z is seconds from
midnight. Points are from GPS carried on all
journeys with static time auto-completed. Model
produced by Earthvision (http//www.dgi.com/)
Courtesy Jonathan Raper of City University
London, GISci 2002 Keynote
7
More Representations in Space/Time
8
Representation in Space/Time

• What would more detail show?

• Infinite complexity Simplification
• must reduce to manageable volume

9
Geographic Representation

• Location, location, location!
• to map, to link based on the same place,
• to measure distances and areas
• Time
• height above sea level (slow?)
• Sea surface temperature (fast)
• Attributes
• physical or environmental
• soci-economic (e.g., population or income)

10
Geographic Representation

• The atom of geographic information
• lt location, time, attribute gt
• Its chilly today in Corvallis
• lt Corvallis, today, chilly gt
• at 44 N, 123 E at 12 noon PST the temperature
  was 60F

11
Atoms of Geographic Information

• an infinite number
• two-word description of every sq km on the
  planet, 10 Gb
• store one number for every sq m, 1 Pb (trillion
  bytes)
• Too much for any system
• How to limit?

12
Limiting Detail

• aggregate, generalize, approximate
• ignore the water?!
• 2/3 of planet!
• one temperature for all of Corvallis
• one number for an entire polygon
• sample the space
• only measure at weather stations, temp. varies
  slowly
• all geographic data miss detail
• all are uncertain to some degree

13
The Problem of Infinite Complexity

• many ways of limiting detail
• a GIS user must make choices
• GIS developers must allow for many options
• Most important option is how we choose to think
  about the world

14
Objects and Fields

• Objects
• Well-defined boundaries in empty space
• Desktop littered w/ objects
• World littered w/ cars, houses, etc.
• Counts
• 49 houses in a subdivision

How many students at OSU? Clouds in sky? Fish in
the sea? Atmospheric highs in N. hemisphere today?
15
Fieldscare to count every peak, valley, ridge,
slope???
16
Fieldswhat varies continuously and how
smoothlymeasurable at every point on a surface

• Radiation captured by satellite
• Elevation
• Temperature
• Soil type
• Soil pH
• Rainfall
• Land cover type
• Ownership

An image of part of the lower Colorado River in
the southwestern USA. The lightness of the image
at any point measures the amount of radiation
captured by the satellite's imaging system.
Image derived from a public domain SPOT image,
courtesy of Alexandria Digital Library,
University of California, Santa Barbara.
17
Field/Raster WorldviewTessellated Ground Plane
Orange County, CA
Courtesy of Russ Michel, Pictometry Intl. Inc.
18
Object/Vector Worldview
Projected with flat ground plane
Projected with tessellated ground plane
Orange County Street Centerlines
Courtesy of Russ Michel, Pictometry Intl. Inc.
19
Fields

• each variable has one value everywhere
• variable is a function of location
• field a way of conceiving of geography as a set
  of variables, each having one value at every
  location on the planet
• zf f (x,y,z,t)

20
Fields and Objects

• Objects are intuitive, part of everyday life
• May overlap
• Fields worth measuring at every point
• Often associated with scientific measurements
• surfaces, fronts, highs, lows
• Both objects and fields can be represented either
  in raster or in vector form

21
One Variable as Pt (grid or sample), TINRaster,
Poly, ContoursWhat changes? Representation or
phenomenon?
22
Ontology

• Ontology the study of the basic elements of
  description
• "what we tell about"
• semantics, semantic interoperability
• discrete objects and fields are two different
  ontologies
• www.ucgis.org
• Research Challenge in Ontology

23
A Coastal Geo-Ontology
Courtesy Jonathan Raper of City University
London, GISci 2002 Keynote
24
Describing LOCATION
25
What constitutes a mountain?

• 1000 ft was magic number but how?

26
ICAN Interoperability Prototypeican.ucc.ie
Starts with metadata interoperability
Mapping of Terms MIDA Coastline is similar
to OCA Shoreline
Coastline
Shoreline
Atlas X
ISO Metadata MIDA terminology
FGDC Metadata OCA terminology
X Standard X terminology

27
Gateway to the Literature

• Goodchild, M. F., M. Yuan, Cova, T. Towards a
  general theory of geographic representation in
  GIS. Int. J. Geog. Inf. Sci. 21(3-4) 239-260,
  2007.
• Comber, A., P.R. Fisher, J., and R. Wadsworth,
  Integrating land-cover data with different
  ontologies Identifying change from
  inconsistency, Int. J. Geog. Inf. Sci., 18 (7),
  691-708, 2004.
• Golledge, R., The Nature of Geographic Knowledge,
  Annals of the AAG, 92(1) 1-14, 2002.
• Kavouras, M., M. Kokla, and E. Tomai, Comparing
  categories among geographic ontologies, Comp.
  Geosci, 31 (2), 145-154, 2005.
• Kuhn, W., Semantic reference systems, Int. J.
  Geog. Inf. Sci., 17 (5), 405-409, 2003.