A short introduction to GIS


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A short introduction to GIS

  1. 1. A Short Introduction to Geographic Information Systems Xiaogang (Marshall) Ma School of Science Rensselaer Polytechnic Institute Tuesday, January 22, 2013 GIS in the Sciences ERTH 4750 (38031)
  2. 2. Acknowledgements • This lecture is partly based on: – Huisman, O., de By, R.A. (eds.), 2009. Principles of Geographic Information Systems. ITC Press, Enschede, The Netherlands – Fox, P., 2012. Introduction to Geographic Information Systems for Science. Course lecture at RPI, Troy 2
  3. 3. Contents • 1 The purpose of GIS • 2 The real world and representations of it • 3 GIS as a domain of science and technology • 4 Seven levels of GIS competence 3
  4. 4. 1 The purpose of GIS • A few example scenarios • An urban planner might like to find out about the urban fringe growth in her/his city, and quantify the population growth that some suburbs are witnessing. S/he might also like to understand why it is these suburbs and not others. Urban fringe, Waitara, New Zealand Image courtesy of Quentin Christie 4
  5. 5. • A biologist might be interested to determine how widespread the invasive Asian clam in Lake George was, and to develop and implement an eradication plan. 1 The purpose of GIS Asian clam identified in Lake George, NY Image courtesy of lakegeorge.com 5
  6. 6. • A geological engineer might want to identify the best localities for constructing buildings in an area with regular earthquakes by looking at rock formation characteristics. 1 The purpose of GIS Rock outcrop, North San Francisco Image courtesy of Pascal Calarco 6
  7. 7. • A forest manager might want to optimize timber production using data on soil and current tree stand distributions, in the presence of a number of operational constraints, such as the requirement to preserve tree diversity. 1 The purpose of GIS Timber production Image courtesy of futureforest.eu 7
  8. 8. 1 The purpose of GIS • Various professionals work with data that relates to space, typically involving positional data. • Positional data determines where things are, or perhaps where they were or will be. Abraham LincolnThomas JeffersonGeorge Washington They worked on ‘positions’ (land survey) before entering politics Images courtesy of wikipedia.org 8
  9. 9. 1 The purpose of GIS • More precisely, those professionals’ questions are related to geographic space, which have positional data relative to the Earth’s surface (georeferenced data). – There are also positional data of a non-geographic nature. • A Geographic Information System (GIS) is a computerized system that helps in maintaining and displaying data about geographic space. 9
  10. 10. 1.1 Some fundamental observations • Our world is constantly changing, and not all changes are for the better. – Natural causes: e.g., volcanic eruptions – Human causes: e.g., land use changes – Mix / Unclear causes: e.g., El Niño / La Niña events Grimsvotn volcano, May 21, 2011 Image courtesy of AP / Jon Gustafsson U.S. Drought of 2012 Image courtesy of The NY Times / Mashid Mohadjerin 10
  11. 11. 1.1 Some fundamental observations • We, humans, want to understand what is going on in our world, and to take action(s). • The fundamental problem in many uses of GIS is that of understanding phenomena that have (a) a geographic dimension, and (b) a temporal dimension. – Spatio-temporal: be of/in space and time “Everything that happens, happens somewhere in space and time. ” -- Michael Wegener (University of Dortmund) 11
  12. 12. 1.1 Some fundamental observations Drought’s Footprint (1930 to present) Image source: National Climatic Data Center, NOAA 12
  13. 13. 1.1 Some fundamental observations The maps show current and projected forest types. Major changes are projected for many regions. For example, in the Northeast, under a mid- range warming scenario, the currently dominant maple-beech-birch forest type is projected to be completely displaced by other forest types in a warmer future. Projected shifts in forest types Image source: http://nca2009.globalchange.gov/ projected-shifts-forest-types 13
  14. 14. 1.2 Definition of GIS • We may distinguish three important phases of working with georeferenced data: – Data preparation and entry – Data analysis – Data presentation • The three phases may be repeated a number of times before we are satisfied with the results. • We can define a GIS as a computerized system that facilitates the phases of data entry, data analysis and data presentation especially in cases when we are dealing with georeferenced data. 14
  15. 15. 1.3 Spatial data and geoinformation • Data are representations that can be operated upon by a computer. • Metadata are data about data. • Spatial data are data that contain positional values. • Geospatial data are spatial data that are georeferenced. – In the context of GIS, spatial data and geospatial data are regarded as synonyms of georeferenced data. • Information is the meaning of data as interpreted by human beings. • Geoinformation is information that involves interpretation of spatial data. 15
  16. 16. 1.3 Spatial data and geoinformation Image courtesy of Peter Fox Data Information Knowledge Context Presentation Organization Integration Conversation Creation Gathering Experience 16
  17. 17. 1.3 Spatial data and geoinformation • In GIS, a wider view of QUALITY is important for several reasons: – Even source data have been subject to strict quality control, errors are introduced when these data are input to a GIS. – A GIS database normally contains data from different sources of varying quality. – Most GIS analysis operations will themselves introduce errors. – Uncertainty in decision-making depends upon quality of base data and derived information. – … … 17
  18. 18. 1.3 Spatial data and geoinformation Comparison of seven available digital databases of the streets in part of Goleta, CA, USA (Goodchild 2011) 18
  19. 19. 2 The real world and representations of it • When dealing with data and information we are usually trying to represent some part of the real world as it is, as it was, or perhaps as we think it will be. – We say ‘some part’ because the real world cannot be represented completely. • We use a computer representation of some part of the real world to enter and store data, analyze the data and transfer results to humans or to other systems. Image courtesy of NOAA 19
  20. 20. 2.1 Modeling • A representation of some part of the real world can be considered a model of that part. – This allows us to study the model instead of the real world. • Models come in many different flavors. – Maps – Databases – … … • Most maps and databases can be considered static models. • Dynamic models or process models address changes that have taken place, are taking place and may take place. 20
  21. 21. 2.1 Modeling Dynamic model: break-up of Pangaea and formation of modern continents Static model: map of Pangaea with present continents outlined Image courtesy of Wikipedia Image courtesy of USGS Pangaea: a supercontinent that existed about 300 million years ago 21
  22. 22. 2.2 Maps • The best known models of the real world are maps. • A map is always a graphic representation at a certain level of detail. – The smaller the scale, the less detail a map can show. • Cartography: science and art of map making Map scale increasing Images made with Google Maps Image © Bil Keane. Courtesy of familycircus.com 22
  23. 23. 2.2 Maps More examples of maps Images courtesy of rpi.edu 23
  24. 24. 2.3 Databases • A database is a repository for storing large amounts of data. – It allows concurrent use. – It supports storage optimization. – It supports data integrity. – It has a query facility. – It offers query optimization. • Modern database systems organize the stored data in tabular format. Image courtesy of MapInfo User Guide 24
  25. 25. 2.3 Databases • A database may have many tables, and each table may have many columns (attributes) and rows (records). • During database design, it is determined which tables will be present and which columns each table will have. • The result of a completed database design is known as the database schema. • To define the database schema, we use a language, commonly known as a data model. • The definition of a model is called data modeling. 25
  26. 26. 2.4 Spatial databases • Spatial databases are a specific type of database. – Besides traditional administrative data, they can store representations of real world geographic phenomena for use in a GIS. – A spatial database, also called a geodatabase, focuses on concurrency, storage, integrity, and querying of spatial data. – A GIS focuses on operating on spatial data with a ‘deep understanding’ of geographic space. • A spatial database is used under the assumption that the relevant spatial phenomena occur in a two- or three- dimensional Euclidean space. 26
  27. 27. 2.4 Spatial databases • Geographic phenomena have various relationships with each other and possess spatial, temporal, and thematic attributes. • For data management purposes, phenomena are classified into thematic data layers. • Spatial analysis is the generic term for all manipulations of spatial data carried out to improve one’s understanding of the geographic phenomena that the data represent. Image courtesy of Jonathan Campbell and Michael Shin 27
  28. 28. 3 GIS as a domain of science and technology (DiBiase et al. 2006) Philosophy Computer Science Mathematics Statistics Psychology Landscape Architecture Engineering Various Application Domains Geography Information Science & Technology Geographic Information Science & Technology Geographic Information Science Application of GI Science & Technology Geospatial Technology From GI System to GI Science & Technology 28
  29. 29. 3.1 Geographic Information Science • Hmm, a broad S – From GISystems to GIScience – GIScience: the science behind GISystems technology • considers fundamental questions raised by the use of systems and technologies • is the science needed to keep technology at the cutting edge Courtesy: http://www.ncgia.ucsb.edu/giscc/units/u002/u002.html 29
  30. 30. 3.2 Geospatial technology • Geospatial technology / Geomatics – Land surveying – Remote sensing – Cartography – Geographic information systems (GIS) – Global navigation satellite systems (GPS, GLONASS, Galileo, Compass) – Photogrammetry – Geography – … 30
  31. 31. • Global Positioning System (GPS) – a system of Earth-orbiting satellites transmitting precisely timed signals • a similar system deployed by the Russian Federation is called GLONASS (global navigation satellite system) • and other systems by EU, China, India, etc. – signals are received by a special electronic device • the smallest versions are hand-held and even smaller – provides direct measurement of position on the Earth's surface – location is expressed in latitude/longitude or other standard system 3.2 Geospatial technology 31
  32. 32. • GPS 3.2 Geospatial technology Image source: AP Image source: Wikipedia Image from WWWImage source: Wikipedia 32
  33. 33. • Remote Sensing (RS) – use of Earth orbiting satellites to capture information about the surface and atmosphere below – satellites vary depending on how much detail can be seen, what parts of the electromagnetic spectrum are sensed – signals transmitted to Earth receiving stations where they are transformed for dissemination as digital images Courtesy: http://www.ncgia.ucsb.edu/giscc/units/u002/u002.html 3.2 Geospatial technology 33
  34. 34. 3.2 Geospatial technology • Two main types of RS – Passive RS: detect natural radiation (e.g., sunlight) that is emitted or reflected by the object or surrounding areas – Active RS: emits energy (e.g., laser light) in order to scan objects and areas whereupon a sensor then detects and measures the radiation that is reflected or backscattered from the target Images from: http://www.rsgisrs.com/rs_types.htm34
  35. 35. 35 Night lights of Australia as observed by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite in April and October 2012
  36. 36. 36 More information: http://earthobservatory.nasa.gov/IOTD/view.php?id=80030&src=fb Fires
  37. 37. • GISystems – a computerized system that facilitates the entry, analysis, and presentation of georeferenced data • GPS and RS are primary data sources for GIS 3.2 Geospatial technology http://shuttles.rpi.edu/ http://www.flightradar24.com/ Try these: 37
  38. 38. 4 Seven levels of GIS competence • Levels of GIS competence in ascending order: 1. Public awareness of GIS and its uses; 2. Basic spatial and computer understanding; 3. Routine use of basic GIS software; 4. Higher-level modeling applications of GIS; 5. Design and development of GIS applications; 6. Design of geographic information systems; and 7. GIS research and development. (DiBiase et al. 2006; Marble 1997) 38
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