Geographic Information Systems GIS SGO1910

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Geographic Information Systems (GIS)SGO1910
SGO4030 Fall 2006
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Announcements

• WUN GIS Seminar "Representations of space-time
  in GIS" by Donna Pequet, Penn State University
• Date Wednesday, October 18, 17.00-19.00
• Place UB (Georg Sverdrups hus) room 3514.
• For more information on this series
  http//www.wun.ac.uk/ggisa/seminars.html

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http//www.wun.ac.uk/ggisa/seminars.html
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Other Resources

• GIS Club
• GIS Day November 15, 2006
• ESRI Brukerkonferanse (February 2007)

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Midterm Quizzes

• The first quiz will be handed back to you at the
  end of class today.
• The next midterm quiz is in two weeks (on Oct.
  31), and will cover chapters 6,9,10,12 and three
  lectures.

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• 22. Geographic techniques can be applied to
  non-geographic spaces. True
• But many of the methods used in GIS are also
  applicable to other non-geographic spaces,
  including the surfaces of other planets, the
  space of the cosmos, and the space of the human
  body that is captured by medical images (p. 8)

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• Jeg er malerikonservator. I 2004-2005 designet og
  ledet jeg et prosjekt på Munch-museet som skulle
  svare på to spørsmål hva vil det koste å sette
  kommunens Munch-malerier i stand, og hvordan skal
  arbeidet prioriteres. Kommunen eier omlag 1150
  Munch-malerier, og alle skulle vurderes i dette
  prosjektet, kalt Konserveringsplanprosjektet.
• Til å tilstandsregistrere og tidsberegne
  behandlingen av maleriene brukte jeg GIS ArcView.
  Prioriteringen av behandlingen av Munch-maleriene
  ble utarbeidet som en matrise basert på
  kunsthistorisk verdi og tilstand (GIS).

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Painting on church ceiling (1270 AD) -- Vestre
Slidre, Oppland
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Oslo Project

• The aim of this project is to integrate what you
  have learned in GIS lectures and labs through
  practical experience. Working in groups of three
  or four, you will address a spatial issue in Oslo
  (e.g. resource distribution, inequality) through
  the collection, mapping and analysis of data,
  which will then be presented in a concise
  professional report that is no more than 12 pages
  long, including maps and references.

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Groups

• You may select your own group, or we can create
  groups for you. Groups should be established over
  the next two weeks send me an email when your
  group is formed.
• Graduate students have the option of doing an
  independent project related to their own
  research, or the Oslo project in a group.

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Acquiring Map Data

• Data sources in Norway

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Global Positioning Systems (GPS)

• Sources of information
• http//www.trimble.com/gps/
• http//www.colorado.edu/geography/gcraft/notes/gps
  /gps.htmlDODSystem
• http//home.no.net/perfrode/Kart/hva_er_gps_paa_no
  rsk.htm

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GPS is a Satellite Navigation System

• GPS is funded by and controlled by the U. S.
  Department of Defense (DOD). While there are many
  thousands of civil users of GPS world-wide, the
  system was designed for and is operated by the U.
  S. military.
• GPS provides specially coded satellite signals
  that can be processed in a GPS receiver, enabling
  the receiver to compute position, velocity and
  time.
• Four GPS satellite signals are used to compute
  positions in three dimensions and the time offset
  in the receiver clock.

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Space Segment

• The Space Segment of the system consists of the
  GPS satellites. These space vehicles (SVs) send
  radio signals from space.

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Space Segment (cont)

• The nominal GPS Operational Constellation
  consists of 24 satellites that orbit the earth in
  12 hours.
• The satellite orbits repeat almost the same
  ground track (as the earth turns beneath them)
  once each day. The orbit altitude is such that
  the satellites repeat the same track and
  configuration over any point approximately each
  24 hours (4 minutes earlier each day).
• There are six orbital planes (with nominally four
  SVs in each), equally spaced (60 degrees apart),
  and inclined at about fifty-five degrees with
  respect to the equatorial plane.
• This constellation provides the user with between
  five and eight SVs visible from any point on the
  earth.

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GPS Satellites Name NAVSTAR Manufacturer
Rockwell International Altitude 10,900 nautical
miles Weight 1900 lbs (in orbit) Size17 ft
with solar panels extended Orbital Period 12
hours Orbital Plane 55 degrees to equatorial
plane Planned Lifespan 7.5 years Current
constellation 24 Block II production satellites
Future satellites 21 Block IIrs developed by
Martin Marietta
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Latest Development

• Galileo, Europe's contribution to the Global
  Navigation Satellite System (GNSS), is creating a
  buzz in the Global Positioning Systems (GPS)
  applications market. With its advantages of
  signal reliability and integrity, it is poised to
  drive European GPS applications markets. Unlike
  its US counterpart, Galileo is envisioned as
  being independent of military control and is
  expected to be harnessed for widespread
  commercial and civilian purposes. (Space Daily,
  Dec. 18, 2003)

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From Wikipedia

• The system should be operational by 2010, two
  years later than originally anticipated.
• The European Commission had some difficulty
  trying to secure funding for the next stage of
  the Galileo project. European states were wary of
  investing the necessary funds at a time of
  economic difficulty, when national budgets were
  being threatened across Europe. Following the
  September 11, 2001 attacks, the United States
  Government wrote to the European Union opposing
  the project, arguing that it would end the
  ability of the U.S. to shut down GPS in times of
  military operations. On January 17, 2002 a
  spokesman for the project somberly stated that,
  as a result of U.S. pressure and economic
  difficulties, "Galileo is almost dead." 1
• A few months later, however, the situation
  changed dramatically. Partially in reaction to
  the pressure exerted by the U.S. Government,
  European Union member states decided it was
  important to have their own independent
  satellite-based positioning and timing
  infrastructure. All European member states became
  strongly in favour of the Galileo system in late
  2002 and, as a result, the project actually
  became over-funded, which posed a completely new
  set of problems for the European Space Agency
  (ESA), as a way had to be found to convince the
  member states to reduce the funding.

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A Happy Ending??

• In June 2004, in signed agreement with the United
  States, the European Union has agreed to switch
  to a range of frequencies known as Binary Offset
  Carrier 1.1, which will allow both European and
  American forces to block each other's signals in
  the battlefield without disabling the entire
  system. The European Union also agreed to address
  the "mutual concerns related to the protection of
  allied and U.S. national security capabilities.
• International involvement China, Israel,
  Ukraine, South Korea, India, Morocco, Saudia
  Arabia, etc.

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Control Segment

• The Control Segment consists of a system of
  tracking stations located around the world.

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The Master Control facility is located at
Schriever Air Force Base (formerly Falcon AFB) in
Colorado. These monitor stations measure signals
from the SVs which are incorporated into orbital
models for each satellites. The models compute
precise orbital data (ephemeris) and SV clock
corrections for each satellite. The Master
Control station uploads ephemeris and clock data
to the SVs. The SVs then send subsets of the
orbital ephemeris data to GPS receivers over
radio signals.
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User Segment

• The GPS User Segment consists of the GPS
  receivers and the user community. GPS receivers
  convert SV signals into position, velocity, and
  time estimates. Four satellites are required to
  compute the four dimensions of X, Y, Z (position)
  and Time. GPS receivers are used for navigation,
  positioning, time dissemination, and other
  research.
• Navigation in three dimensions is the primary
  function of GPS. Navigation receivers are made
  for aircraft, ships, ground vehicles, and for
  hand carrying by individuals.

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• Precise positioning is possible using GPS
  receivers at reference locations providing
  corrections and relative positioning data for
  remote receivers. Surveying, geodetic control,
  and plate tectonic studies are examples.

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Here's how GPS works in five logical steps

• The basis of GPS is "triangulation" from
  satellites.
• To "triangulate," a GPS receiver measures
  distance using the travel time of radio signals.
• To measure travel time, GPS needs very accurate
  timing which it achieves with some tricks.
• Along with distance, you need to know exactly
  where the satellites are in space. High orbits
  and careful monitoring are the secret.
• Finally you must correct for any delays the
  signal experiences as it travels through the
  atmosphere.

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Triangulating

• Position is calculated from distance measurements
  (ranges) to satellites. 
• Mathematically we need four satellite ranges to
  determine exact position. 
• Three ranges are enough if we reject ridiculous
  answers or use other tricks. 
• Another range is required for technical reasons
  to be discussed later.

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Measuring Distance

• Distance to a satellite is determined by
  measuring how long a radio signal takes to reach
  us from that satellite. 
• To make the measurement we assume that both the
  satellite and our receiver are generating the
  same pseudo-random codes at exactly the same
  time. 
• By comparing how late the satellite's
  pseudo-random code appears compared to our
  receiver's code, we determine how long it took to
  reach us. 
• Multiply that travel time by the speed of light
  and you've got distance.

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Getting Perfect Timing

• Accurate timing is the key to measuring distance
  to satellites. 
• Satellites are accurate because they have atomic
  clocks on board. 
• Receiver clocks don't have to be too accurate
  because an extra satellite range measurement can
  remove errors.

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2005 Nobel Prize in Physics

• Two physicists (Hall and Haensch) shared the
  Nobel Prize in Physics for advancing the
  development of laser-based precision
  spectroscopy, a field that opens the way to the
  next generation of global positioning system
  (GPS) navigation and ultra-precise atomic clocks.

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Satellite Positions

• To use the satellites as references for range
  measurements we need to know exactly where they
  are. 
• GPS satellites are so high up their orbits are
  very predictable. 
• Minor variations in their orbits are measured by
  the U.S. Department of Defense. 
• The error information is sent to the satellites,
  to be transmitted along with the timing signals.

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• Three satellites could be used determine three
  position dimensions with a perfect receiver
  clock. In practice this is rarely possible and
  three SVs are used to compute a two-dimensional,
  horizontal fix (in latitude and longitude) given
  an assumed height. This is often possible at sea
  or in altimeter equipped aircraft.
• Five or more satellites can provide position,
  time and redundancy. More SVs can provide extra
  position fix certainty and can allow detection of
  out-of-tolerance signals under certain
  circumstances.

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• Position in XYZ is converted within the receiver
  to geodetic latitude, longitude and height above
  the ellipsoid.
• Latitude and longitude are usually provided in
  the geodetic datum on which GPS is based
  (WGS-84). Receivers can often be set to convert
  to other user-required datums. Position offsets
  of hundreds of meters can result from using the
  wrong datum.

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GPS errors are a combination of noise, bias,
blunders.
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Selective Availability (SA)

• SA is the intentional degradation of the SPS
  signals by a time varying bias. SA is controlled
  by the DOD to limit accuracy for non-U. S.
  military and government users.
• SA was turned off in May, 2000!

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Bias Error sources

• SV clock errors uncorrected by Control Segment
  1 meter
• Ephemeris data errors 1 meter
• Tropospheric delays 1 meter. The troposphere is
  the lower part (ground level to from 8 to 13 km)
  of the atmosphere that experiences the changes in
  temperature, pressure, and humidity associated
  with weather changes. Complex models of
  tropospheric delay require estimates or
  measurements of these parameters.
• Unmodeled ionosphere delays 10 meters. The
  ionosphere is the layer of the atmosphere from 50
  to 500 km that consists of ionized air. The
  transmitted model can only remove about half of
  the possible 70 ns of delay leaving a ten meter
  un-modeled residual.
• Multipath 0.5 meters. Multipath is caused by
  reflected signals from surfaces near the receiver
  that can either interfere with or be mistaken for
  the signal that follows the straight line path
  from the satellite. Multipath is difficult to
  detect and sometime hard to avoid.

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Blunders can result in errors of hundred of
kilometers.

• Control segment mistakes due to computer or human
  error can cause errors from one meter to hundreds
  of kilometers.
• User mistakes, including incorrect geodetic datum
  selection, can cause errors from 1 to hundreds of
  meters.
• Receiver errors from software or hardware
  failures can cause blunder errors of any size.

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Correcting Errors

• The earth's ionosphere and atmosphere cause
  delays in the GPS signal that translate into
  position errors.
• Some errors can be factored out using mathematics
  and modeling. 
• The configuration of the satellites in the sky
  can magnify other errors. 
• Differential GPS can eliminate almost all error.

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• GPS technology has matured into a resource that
  goes far beyond its original design goals. These
  days scientists, sportsmen, farmers, soldiers,
  pilots, surveyors, hikers, delivery drivers,
  sailors, dispatchers, lumberjacks, fire-fighters,
  and people from many other walks of life are
  using GPS in ways that make their work more
  productive, safer, and sometimes even easier.

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Location Where am I?

• The first and most obvious application of GPS is
  the simple determination of a "position" or
  location. GPS is the first positioning system to
  offer highly precise location data for any point
  on the planet, in any weather. That alone would
  be enough to qualify it as a major utility, but
  the accuracy of GPS and the creativity of its
  users is pushing it into some surprising realms.

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Navigation Where am I going?

• GPS helps you determine exactly where you are,
  but sometimes important to know how to get
  somewhere else. GPS was originally designed to
  provide navigation information for ships and
  planes. So it's no surprise that while this
  technology is appropriate for navigating on
  water, it's also very useful in the air and on
  the land.
• The sea, one of our oldest channels of
  transportation, has been revolutionized by GPS,
  the newest navigation technology.

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• By providing more precise navigation tools and
  accurate landing systems, GPS not only makes
  flying safer, but also more efficient. With
  precise point-to-point navigation, GPS saves fuel
  and extends an aircraft's range by ensuring
  pilots don't stray from the most direct routes to
  their destinations.
• GPS accuracy will also allow closer aircraft
  separations on more direct routes, which in turn
  means more planes can occupy our limited
  airspace. This is especially helpful when you're
  landing a plane in the middle of mountains. And
  small medical evac helicopters benefit from the
  extra minutes saved by the accuracy of GPS
  navigation.

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• Finding your way across the land is an ancient
  art and science. The stars, the compass, and good
  memory for landmarks helped you get from here to
  there. Even advice from someone along the way
  came into play. But, landmarks change, stars
  shift position, and compasses are affected by
  magnets and weather. And if you've ever sought
  directions from a local, you know it can just add
  to the confusion. The situation has never been
  perfect.
• Today hikers, bikers, skiers, and drivers apply
  GPS to the age-old challenge of finding their
  way.

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• In 1994 Norwegian Borge Ousland reached the
  North Pole after skiing 1000 kilometers from
  Siberia alone and unsupported. For this
  incredible challenge Børge carried a bible to
  read, some Jimi Hendrix to listen to, and a
  Trimble Scout GPS receiver to help find his way.
  

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Tracking

• Commerce relies on fleets of vehicles to deliver
  goods and services either across a crowded city
  or through nationwide corridors. So, effective
  fleet management has direct bottom-line
  implications, such as telling a customer when a
  package will arrive, spacing buses for the best
  scheduled service, directing the nearest
  ambulance to an accident, or helping tankers
  avoid hazards.
• GPS used in conjunction with communication links
  and computers can benefit applications in
  agriculture, mass transit, urban delivery, public
  safety, and vessel and vehicle tracking. So it's
  no surprise that police, ambulance, and fire
  departments are adopting GPS-based AVL (Automatic
  Vehicle Location) Manager to pinpoint both the
  location of the emergency and the location of the
  nearest response vehicle on a computer map. With
  this kind of clear visual picture of the
  situation, dispatchers can react immediately and
  confidently.

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Timing

• Although GPS is well-known for locating,
  navigation, and tracking, it's also used to
  disseminate precise time, time intervals, and
  frequency. Time is a powerful commodity, and
  exact time is more powerful still. Knowing that a
  group of timed events is perfectly synchronized
  is often very important. GPS makes the job of
  "synchronizing our watches" easy and reliable.
• There are three fundamental ways we use time. As
  a universal marker, time tells us when things
  happened or when they will. As a way to
  synchronize people, events, even other types of
  signals, time helps keep the world on schedule.
  And as a way to tell how long things last, time
  provides and accurate, unambiguous sense of
  duration.
• GPS satellites carry highly accurate atomic
  clocks. And in order for the system to work, our
  GPS receivers here on the ground synchronize
  themselves to these clocks. That means that every
  GPS receiver is, in essence, an atomic accuracy
  clock.

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Mapping

• Using GPS to survey and map it precisely saves
  time and money in this most stringent of all
  applications. Today, GPS makes it possible for a
  single surveyor to accomplish in a day what used
  to take weeks with an entire team. And they can
  do their work with a higher level of accuracy
  than ever before.
• GPS technology is now the method of choice for
  performing control surveys, and the effect on
  surveying in general has been considerable. GPS
  pinpoints a position, a route, and a fleet of
  vehicles. Mapping is the art and science of using
  GPS to locate items, then create maps and models
  of everything in the world. Mountains, rivers,
  forests and other landforms. Roads, routes, and
  city streets. Endangered animals, precious
  minerals and all sorts of resources. Damage and
  disasters, trash and archeological treasures. GPS
  is mapping the world.

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Geographic Databases
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A GIS can answer the question What is where?

• WHAT Characteristics of attributes or features.
• WHERE In geographic space.

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A GIS links attribute and spatial data

• Attribute Data
• Flat File
• Relations

• Map Data
• Point File
• Line File
• Area File
• Topology

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Flat File Database
Attribute
Attribute
Attribute
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Arc/node map data structure with files
13
1 x y
11
e
2 x y
l
i
12
3 x y
F

10
2
s
4 x y
t
7
n
5 x y
i
5
o
POLYGON A
6 x y
P
9
7 x y
4
8 x y
6
1
9 x y
2
10 x y
3
11 x y
8
12 x y
13 x y
1
File of Arcs by Polygon
1
1,2,3,4,5,6,7
A
1,2
, Area, Attributes
2
1,8,9,10,11,12,13,7
Arcs File
Figure 3.4
Arc/Node Map Data Structure with Files.
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What is a Data Model?

• A logical construct for the storage and retrieval
  of information.
• Attribute data models are needed for the DBMS.
• The origin of DBMS data models is in computer
  science.

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Definitions

• Database an integrated set of data on a
  particular subject
• Geographic (spatial) database - database
  containing geographic data of a particular
  subject for a particular area
• Database Management System (DBMS) software to
  create, maintain and access databases

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A DBMS contains

• Data definition language
• Data dictionary
• Data-entry module
• Data update module
• Report generator
• Query language

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Advantages of Databases

• Avoids redundancy and duplication
• Reduces data maintenance costs
• Applications are separated from the data
• Applications persist over time
• Support multiple concurrent applications
• Better data sharing
• Security and standards can be defined and
  enforced

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Disadvantages of Databases

• Expense
• Complexity
• Performance especially complex data types
• Integration with other systems can be difficult

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Characteristics of DBMS (1)

• Data model support for multiple data types
• e.g MS Access supports Text, Memo, Number,
  Date/Time, Currency, AutoNumber, Yes/No, OLE
  Object, Hyperlink, Lookup Wizard
• Load data from files, databases and other
  applications
• Index for rapid retrieval

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Characteristics of DBMS (2)

• Query language SQL
• Security controlled access to data
• Multi-level groups
• Controlled update using a transaction manager
• Backup and recovery

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Role of DBMS
Task
System

• Data load
• Editing
• Visualization
• Mapping
• Analysis

Geographic Information System

• Storage
• Indexing
• Security
• Query

Database Management System
Data
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Retrieval

• The ability of the DBMS or GIS to get back on
  demand data that were previously stored.
• Geographic search is the secret to GIS data
  retrieval.
• Many forms of data organization are incapable of
  geographic search.
• GIS systems have embedded DBMSs, or link to a
  commercial DBMS.

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Types of DBMS Model

• Hierarchical
• Network
• Relational - RDBMS
• Object-oriented - OODBMS
• Object-relational - ORDBMS

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Historically, databases were structured
hierarchically in files...
Norge
Akershus
Oppland
Hordaland
Asker
Bærum
Ski
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Relational DBMS

• Data stored as tuples (tup-el), conceptualized as
  tables
• Table data about a class of objects
• Two-dimensional list (array)
• Rows objects
• Columns object states (properties, attributes)

Tuple??? A row in a relational table synonymous
with record, observation. A set of elements.
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Relation Rules

• Only one value in each cell (intersection of row
  and column)
• All values in a column are about the same subject
• Each row is unique
• No significance in column sequence
• No significance in row sequence

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Table
Column property
Table Object Class
Row object
Object Classes with Geometry called Feature
Classes
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Relational Join

• Fundamental query operation
• Table joins use common keys (column values)
• Table (attribute) join concept has been extended
  to geographic case

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Relational Data Bases
File
Patient Record
Key Check-in
Check Out
Room No.
42
2/1/96
2/4/96
N763
78
2/3/96
2/4/96
N712
Purchase Record
File
Item
Date
Price
Customer
Key
Skate Board
2/1/96
49.95
John Smith
42
Baseball Bat
2/1/96
17.99
James Brown
978
File
Accident Report
Date
Injury
Name
Key
Location
2/1/96
Broken Leg
John Smith
42
75 Elm Street
2/2/96
Concussion
Sylvia Jones
654
12 State Street
2/2/96
Cut on Ear
Robert Doe
123
2323 Broad Street
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Most DBMS are now relational databases.

• Based on multiple flat files for records, with
  dissimilar attribute structures, connected by a
  common key attribute.

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Retrieval Operations

• Searches by attribute find and browse.
• Data reorganization select, renumber, and sort.
• Compute allows the creation of new attributes
  based on calculated values.

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Spatial Retrieval Operations

• Attribute queries are not very useful for
  geographic search.
• In a map database the records are features.
• The spatial equivalent of a find is locate, the
  GIS highlights the result.
• Spatial equivalents of the DBMS queries result
  in locating sets of features or building new GIS
  layers.

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The Retrieval User Interface

• GIS query is usually by command line, batch, or
  macro.
• Most GIS packages use the GUI of the computers
  operating system to support both a menu-type
  query interface and a macro or programming
  language.
• SQL is a standard interface to relational
  databases and is supported by many GISs.

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SQL

• Structured (Standard) Query Language
  (pronounced SEQUEL)
• Developed by IBM in 1970s
• Now de facto and de jure standard for accessing
  relational databases
• Three types of usage
• Stand alone queries
• High level programming
• Embedded in other applications

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Types of SQL Statements

• Data Definition Language (DDL)
• Create, alter and delete data
• CREATE TABLE, CREATE INDEX
• Data Manipulation Language (DML)
• Retrieve and manipulate data
• SELECT, UPDATE, DELETE, INSERT
• Data Control Languages (DCL)
• Control security of data
• GRANT, CREATE USER, DROP USER

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Spatial Relations

• Equals same geometries
• Disjoint geometries share common point
• Intersects geometries intersect
• Touches geometries intersect at common boundary
• Crosses geometries overlap
• Within geometry within
• Contains geometry completely contains
• Overlaps geometries of same dimension overlap
• Relate intersection between interior, boundary
  or exterior

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Spatial Methods

• Distance shortest distance
• Buffer geometric buffer
• ConvexHull smallest convex polygon geometry
• Intersection points common to two geometries
• Union all points in geometries
• Difference points different between two
  geometries
• SymDifference points in either, but not both of
  input geometries

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Spatial Search

• Buffering is a spatial retrieval around points,
  lines, or areas based on distance.
• Overlay is a spatial retrieval operation that is
  equivalent to an attribute join.

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Identify
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Recode
OR
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Data overlay
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Overlay
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Types of overlay operations

• And
• Or
• Max
• Min

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Buffer (raster)
1
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Buffer (vector)
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Complex Retrieval Map Algebra

• Combinations of spatial and attribute queries can
  build some complex and powerful GIS operations,
  such as weighting.

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Summary

• Database an integrated set of data on a
  particular subject
• Databases offer many advantages over files
• Relational databases dominate