Geog 176B Lecture 2: Representing Geography [Text: Ch. 3] A map is a representation Why do we use representations How do we gather in as long as mation Mike Goodchild’s Counties Visited 5 billion years

Geog 176B Lecture 2: Representing Geography [Text: Ch. 3] A map is a representation Why do we use representations How do we gather in as long as mation Mike Goodchild’s Counties Visited 5 billion years www.phwiki.com

Geog 176B Lecture 2: Representing Geography [Text: Ch. 3] A map is a representation Why do we use representations How do we gather in as long as mation Mike Goodchild’s Counties Visited 5 billion years

Foley, Mike, Hot Topic & Product Editor; Site Founder has reference to this Academic Journal, PHwiki organized this Journal Geog 176B Lecture 2: Representing Geography [Text: Ch. 3] http://www.mondodisotto.it/imageiraq/ A map is a representation Geometry is orthographic in addition to scaled Features are symbolized Why do we use representations How do we gather in as long as mation 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

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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 in as long as mation to: decide where to go as tourists, shoppers run large corporations manage agriculture, as long as estry choose where to live Travel from A to B Underst in addition to geography! All such in as long as mation must use a representation What is communicated is a representation of the real thing Locations in time in addition to space are reduced to a few symbols Communication requires simplification The real world is infinitely complex So representations reduce in as long as mation to a manageable volume

Representations occur: In the human mind, in memory in addition to reasoning (e = m c2) In speech (e.g. acromyns) In written text (abbreviations, etc.) In photographs In digital databases in addition to in GIS Digital representation Much (most) human communication is now digital sent through a “pipe” or transmission channel that can transmit only 0s in addition to 1s stored on devices that can store only 0s in addition to 1s processed as 0s in addition to 1s text in email, word processors uses ASCII (1 & 0) voice in telephone music on CD DVD, digital TV FAX

Digits, distance, in addition to communication When two humans communicate at a distance, chances are the content is expressed at some point in digital as long as m 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 in addition to 1 To all intents in addition to purposes “digital”=“binary” The digital translation challenge How can we express knowledge exclusively in 0s in addition to 1s How can we describe what we know about the world in 0s in addition to 1s How do we capture complex earth features as representations

Digital vs Analog analog in as long as mation expressed by scaling quantities good as long as quantitative in as long as mation a paper map is analog world is scaled to a miniature representation representative fraction is key, e.g. 1:24,000 digital in as long as mation expressed by symbols requires a coding scheme of representation in symbols sender in addition to 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 in as long as mation: GIS data models in addition to 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 Communication of in as long as mation via a channel Claude Shannon’s Model C. E. Shannon: A mathematical theory of communication. Bell System Technical Journal, vol. 27, pp. 379–423 in addition to 623–656, July in addition to October, 1948. How efficient is the channel of communication Is there in as long as mation that can’t be expressed, e.g. in text What are the limits of a GIS as a communication channel What in as long as mation about a place can’t be expressed in GIS Is the message optimally expressed in the coding system What if the sender in addition to receiver can’t underst in addition to each other different language different alphabet different GIS different data model

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Geographic Representation Geographic in as long as mation in as long as mation about some place on the surface of the Earth or near the surface at some point in time one of the earliest as long as ms of shared in as long as mation hunters in addition to gatherers reporting back to the b in addition to early stick maps as long as navigation in the Pacific drawings on cave walls Ancient geographical representations Source: http://www.khadijateri.com/tribes4.jpg http://bernard.pitzer.edu/~dsegal/1492/FIGURES/ Libyan cave paintings Marshall Isl in addition to s Stick Chart And it’s so different today!

Enter paper the printing press in the 15th Century in as long as mation accessible to all shared knowledge as a human community asset Book: Prince Henry the Navigator, 1394-1460 Global internet use An atom of geographic in as long as mation “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

One geodatabase can have multiple representations of a feature

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