Geog 176B Lecture 2: Representing Geography

[Text: Ch. 3]

http://www.mondodisotto.it/imageiraq/

A map is a representationGeometry is orthographic and scaled

Features are symbolized

Why do we use representations?How do we gather information?

• Limits on human senses• Sight

– Visible spectrum (400-800 nm)– LOS, Horizon, Visibility

• Sound– Audible spectrum (50-15K Hz)– Range to 100m

• Taste, touch, smell– Rather limited spatial range– Limited sensory distinction

Everything else we know about the world we know through communication

• text

• speech

• maps

• photographs

• radio, TV

• Internet

• databases

Knowledge of the surface of the Earth

• 500,000,000 sq km• On average 100 sq m is sensed directly at any

point in time• Odds of being in the right place at the right time• p=100/500,000,000,000,000= 0.000 000 000 000 2

• Odds are trillions to one

• Lotto odds are 25.8 million to one

• Can extend that through migration, travel

Mike Goodchild’s Counties Visited

5 billion years

• If we live through 70

• p=70/5,000,000,000=0.000 000 014

• So, we can know almost nothing about the surface of the Earth via our senses alone

We rely on communicated information to:

• decide where to go as tourists, shoppers

• run large corporations

• manage agriculture, forestry

• choose where to live

• Travel from A to B

• Understand geography!

All such information must use a representation

• What is communicated is a representation of the real thing

• Locations in time and space are reduced to a few symbols

• Communication requires simplification• The real world is infinitely complex• So representations reduce information to a

manageable volume

Representations occur:

• In the human mind, in memory and reasoning (e = m c2)

• In speech (e.g. acromyns)

• In written text (abbreviations, etc.)

• In photographs

• In digital databases

• and in GIS

Digital representation

Much (most?) human communication is now digital

• sent through a "pipe" or transmission channel that can transmit only 0s and 1s

• stored on devices that can store only 0s and 1s• processed as 0s and 1s• text in email, word processors uses ASCII (1 & 0)• voice in telephone• music on CD• DVD, digital TV• FAX

Digits, distance, and communication

• When two humans communicate at a distance, chances are the content is expressed at some point in digital form

• The further the distance the more likely the communication is digital

• The longer/denser the communication, the more likely it is digital

Digital

• From "digit" meaning finger

• A character in a counting system

• How many symbols?

• 0 thru 9, A-Z, a-z, etc.

• All can reduce to 0 and 1

• To all intents and purposes "digital"=“binary”

The digital translation challenge

• How can we express knowledge exclusively in 0s and 1s?

• How can we describe what we know about the world in 0s and 1s?

• How do we capture complex earth features as representations?

Digital vs Analog analog

– information expressed by scaling quantities– good for quantitative information– a paper map is analog– world is scaled to a miniature representation– representative fraction is key, e.g. 1:24,000

digital– information expressed by symbols– requires a coding scheme of representation in symbols– sender and receiver must agree on the scheme– what does digital scale mean?

Digital Coding of Text

• ASCII code one code per character

• A = 65, B = 66, etc.

• 26 letters plus common symbols

• originally 128, extended to 256

• 8 binary digits (one byte) per character

Digital equivalents

• Images: JPEG, TIFF, GIF, BMP, ...

• Sound: MIDI, MP3, WAV

• FAX: CCITT

• Maps, geographic information: GIS data models and structures

Digital coding schemes important in GIS

• ASCII– eight bits per character, names, text annotation

• integer– 3 bits per decimal digit, n bits give 2^n options, or 32 bits per

whole number (short, long integer)

• float (single precision)– 1 sign bit, 7 exponent bits (-63 to +63), 24 mantissa bits (8

significant digits)

• double precision– 1 sign bit, 7 exponent bits, 56 mantissa bits (18 significant

digits)

• BLOB binary large object

What if you received this message:

0100 1000 0110 0101 0110 1100 0110 1100 0110 1111 0010 0000 0111 0111 0110 1111 0111 0010 0110 1100 0110 0100

The Message on Voyager <http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html>

Communication of information via a channel

• Claude Shannon’s Model• C. E. Shannon: A mathematical theory of communication. Bell System Technical Journal, vol. 27,

pp. 379–423 and 623–656, July and October, 1948.

How efficient is the channel of communication?

• Is there information that can't be expressed, e.g. in text• What are the limits of a GIS as a communication channel?• What information about a place can't be expressed in GIS?• Is the message optimally expressed in the coding system?• What if the sender and receiver can't understand each

other?different languagedifferent alphabetdifferent GISdifferent data model

Geographic Representation

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– early stick maps for navigation in the Pacific– drawings on cave walls

Ancient geographical representations

Source: http://www.khadijateri.com/tribes4.jpghttp://bernard.pitzer.edu/~dsegal/1492/FIGURES/

Libyan cave paintingsMarshall Islands Stick Chart

And it’s so different today!

Enter paper

• the printing press in the 15th Century• information accessible to all• shared knowledge as a human community

asset• Book: Prince Henry the Navigator, 1394-

1460

Global internet useWorld RegionsSource:www.internetworldstats.com

 

Population( 2005 Est.)

Population

% of World

Internet Usage,Latest Data

% Users Usage% of

World

Usage Growth

2000-2005

Africa 896,721,874 14.0 % 23,917,500 2.7 % 2.5 % 429.8 %

Asia 3,622,994,130 56.4 % 332,590,713 9.2 % 34.2 % 191.0 %

Europe 804,574,696 12.5 % 285,408,118 35.5 % 29.3 % 171.6 %

Middle East 187,258,006 2.9 % 16,163,500 8.6 % 1.7 % 392.1 %

North America 328,387,059 5.1 % 224,103,811 68.2 % 23.0 % 107.3 %

Latin America/Caribbean 546,723,509 8.5 % 72,953,597 13.3 % 7.5 % 303.8 %

Oceania / Australia 33,443,448 0.5 % 17,690,762 52.9 % 1.8 % 132.2 %

WORLD TOTAL 6,420,102,722 100.0 % 972,828,001 15.2 % 100.0 % 169.5 

An atom of geographic information

• <location, time, attribute>

“It's mild today in Santa Barbara”

Vs.

At 34°25'33" North, 119°42'51" West at noon PST the temperature was 14 Celsius

Standardization

• general methods for describing location• everyone around the world understands latitude

and longitude• similarly for time (International Meridian

Conference 1884)• attributes must also be generally understood

– “mild" is subjective and relative– -14 Celsius is generally understood

• Did Hugh Grant climb a hill or a mountain?

The Englishman Who Went Up a Hill But Came Down a Mountain (1995)

Two English cartographers visit the small South Wales village of Ffynnon Garw, to measure what is claimed to be the "first mountain inside of Wales". It's 1917, and the war in Europe continues. The villagers are very proud of their "mountain", and are understandably dissapointed and furious to find that it is in fact a "hill". Not to be outwitted by a rule (and the Englishmen who enforce it), the villagers set out to make their hill into a mountain, but to do so they must keep the English from leaving, before the job is done.

Source: http://www.imdb.com/title/tt0112966

Hill: A well-defined natural elevation smaller than a mountain.

Suppose we could capture it all

• A complete representation of the planet

• Past, present, and future

• A "mirror world“

• Douglas Adam’s computer for the search for the ultimate question whose answer is 42

• AKA Digital Earth

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 square meter on the

planet would require 1 Petabyte (=1000 Terabytes = 1,000,000 gigabytes= 1 billion megabytes

• That's too many for any current computing system• How do we limit file size?

Reduce the level of detail, aggregate, generalize, approximate

• Ignore the water that's 2/3 of the planet• One temperature for all of California 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

Objects and Fields

• Given that (1) we must digitally represent the world to gather (gain) knowledge about it and (2) all representations of the earth are imperfect; then

• The most important of the options is how we think about (and model) the world

• Cartographic representation led to the feature model

• Remote sensing led to the field model• Both are useful

The Cartographic Heritage

Discrete objects

• Point, lines, areas (or volumes) having known properties

• Littering an otherwise empty space– Objects can be manipulated/edited– Objects can be found in the real world– Objects may overlap– Objects can be counted

Favoring Measurement: Fields

• Things it's worth measuring at every location on the planet

temperature soil pH soil type land cover type elevation rainfall tax rates

Fields

• Fields contain variables that have one value everywhere

• The value of the 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)

Can represent one variable as:

• polygons

• grids

• TIN

• sample points

• contours

Fields and Objects

• Objects are intuitive, part of everyday life

• Fields are more associated with science and measurement

• Both objects and fields can be represented either in raster or in vector form

• Both may need to coexist in a GIS

One geodatabase can have multiple representations of a feature