LECTURE 2: GEOGRAPHIC REPRESENTATION

1. GEOGRAPHIC REPRESENTATION

2. THE FUNDAMENTAL PROBLEM

3. OBJECTS AND FIELDS

Geographic information

information about some place on the surface of the Earth

or near the surface

at some point in time

one of the earliest forms of shared information

hunters and gatherers reporting back to the band

"there's good hunting near the old tree"

early stick maps for navigation in the Pacific

drawings on cave walls

storing on paper

the printing press in the 15th Century

information accessible to all

shared knowledge as a human community asset

Prince Henry the Navigator, 1394-1460

Lisbon monument to the Discoveries

azuleja at Paco de Arcos

who would be on his team today?

The Internet

massive new capability for sharing, communicating geographic information

in digital form

The atom of geographic information

<location, time, attribute>

it's cold today in Ottawa

at 45 North, 75 East at 12 noon EST the temperature was -10 Celsius

general methods for describing location

everyone around the world understands latitude and longitude

similarly for time

attributes must also be generally understood

"cold" is subjective and relative

-10 Celsius is generally understood

did Hugh Grant climb a hill or a mountain?

Suppose we could capture it all

complete representation of the planet

past, present, and future

a "mirror world"

“Imagine, for example, a young child going to a Digital Earth exhibit at a local museum. After donning a head-mounted display, she sees Earth as it appears from space. Using a data glove, she zooms in, using higher and higher levels of resolution, to see continents, then regions, countries, cities, and finally individual houses, trees, and other natural and man-made objects. Having found an area of the planet she is interested in exploring, she takes the equivalent of a ‘magic carpet ride’ through a 3-D visualization of the terrain. Of course, terrain is only one of the numerous kinds of data with which she can interact. Using the system’s voice recognition capabilities, she is able to request information on land cover, distribution of plant and animal species, real-time weather, roads, political boundaries, and population. She can also visualize the environmental information that she and other students all over the world have collected as part of the GLOBE project. This information can be seamlessly fused with the digital map or terrain data. She can get more information on many of the objects she sees by using her data glove to click on a hyperlink. To prepare for her family’s vacation to Yellowstone National Park, for example, she plans the perfect hike to the geysers, bison, and bighorn sheep that she has just read about. In fact, she can follow the trail visually from start to finish before she ever leaves the museum in her hometown.
She is not limited to moving through space, but can also travel through time. After taking a virtual field-trip to Paris to visit the Louvre, she moves backward in time to learn about French history, perusing digitized maps overlaid on the surface of the Digital Earth, newsreel footage, oral history, newspapers and other primary sources. She sends some of this information to her personal e-mail address to study later. The time-line, which stretches off in the distance, can be set for days, years, centuries, or even geological epochs, for those occasions when she wants to learn more about dinosaurs.” (U.S. Vice President Al Gore, in a speech written for presentation at the California Science Museum, Los Angeles, January 1998)

International Society for Digital Earth, ISDE

How many atoms are there?

an infinite number

to make a two-word description of every sq km on the planet would require 10 Gigabytes

to store one number for every sq m on the planet would require 1 Petabyte

how to limit?

ignore the water

that's 2/3 of the planet

one temperature for all of Ottawa

one number for an entire polygon

sample the space

only measure at weather stations

because temperature varies slowly

all geographic data miss detail

all are uncertain to some degree

there are many ways of doing this

a GIS user must make choices

GIS designers must allow for many options

geographic description is complex

The most important of the options

how we think about the world

points, lines, areas (or volumes) having known properties

littering an otherwise empty space

can be manipulated/edited

can be found in the real world

may overlap

can be counted

how many people living in Santa Barbara?

how many vehicles in California?

how many trees growing on the UCSB campus?

how many lakes are there in Minnesota?

how many mountains in Scotland over 3000 ft?

how many clouds in the sky?

how many cities over 1 million population?

how many atmospheric lows in the northern hemisphere today?

represent as shapefiles

things it's worth measuring at every location on the planet

temperature

soil pH

soil type

land cover type

elevation

rainfall

ownership

example image

another example

 each of these variables 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

z = f(x,y,z,t)

represent one variable as:

polygons

raster

TIN

sample points

contours

six methods in all

number of such objects is property of the representation, not the phenomenon

cannot be manipulated

cannot overlap

how many are there?

fronts, highs, lows, or pressure surfaces?

fields are more associated with science

Ontology: the study of the basic elements of description

"what we tell about"

discrete objects and fields are two different ontologies