Gis Concepts 1/5

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Introduction to basic concepts on Geographical Information Systems
Autor: Msc. Alexander Mogollón Diaz
http://www.agronomia.unal.edu.co

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Gis Concepts 1/5

  1. 1. Concepts and Functions of Geographic Information Systems (1/5) MSc GIS - Alexander Mogollon Diaz Department of Agronomy 2009
  2. 2. Concepts and Functions of GIS .PPT Topic #1 Topic #2 Topic #3 1 A GIS is an information system GIS is a technology 2 Spatial Data modelling Sources of data for geodatasets Metadata 3 Geo-referencing Coordinate transformations 4 Database management 5 Spatial Analysis
  3. 3. Maps <ul><li>Are the traditional instrument to describe the world as it was, is, will (probably) be, we want it to be </li></ul><ul><ul><li>Topographic and thematic maps </li></ul></ul><ul><ul><li>Cadastral plans </li></ul></ul><ul><ul><li>Photo-maps, Satellite image based maps </li></ul></ul>
  4. 4. Map scale = 1:50.000
  5. 5. Photo scale = 1:10.000
  6. 6. Plan scale = 1:2.500
  7. 7. Maps <ul><li>Display the location and shape of entities of the real world (geographic reality) </li></ul><ul><li>Describe the state of geographic reality at a given moment in time </li></ul><ul><li>Give meaning to displayed entities by symbolisation according to a map legend </li></ul><ul><li>Information content is related to map scale </li></ul><ul><li>Are static, difficult to update </li></ul>
  8. 8. Plans / Sketches <ul><li>Plans and sketches are the traditional instruments to describe the world as we want it to be </li></ul>
  9. 9. Plan scale = 1:2.500
  10. 10. Spatial databases <ul><li>With the advent of GIS-technology, a new instrument is introduced: the spatial database </li></ul><ul><li>Data describing geographic reality are no longer stored in maps, plans and sketches but in digital databases </li></ul><ul><li>GIS-software provides tools to create and work with spatial databases to </li></ul><ul><ul><li>produce maps … </li></ul></ul><ul><ul><li>enhance knowledge </li></ul></ul><ul><ul><li>support decisions </li></ul></ul>
  11. 11. From data collection to database A/D conversion Structuring Computing functions Other functions Data collection Database Information System
  12. 12. From data collection to database <ul><li>Data about entities : </li></ul><ul><li>persons </li></ul><ul><li>associations </li></ul><ul><li>companies </li></ul><ul><li>licences </li></ul><ul><li>invoices </li></ul><ul><li>municipalities, districts </li></ul><ul><li>properties, … </li></ul>
  13. 13. Data about entities <ul><li>Persons </li></ul><ul><li>Associations </li></ul><ul><li>Companies </li></ul><ul><li>Invoices </li></ul><ul><li>Insurance contracts </li></ul><ul><li>Provinces </li></ul><ul><li>Parcels </li></ul><ul><li>Buildings </li></ul><ul><li>… . </li></ul><ul><li>Date of birth, ... </li></ul><ul><li>List of members, ... </li></ul><ul><li>List of employees, ... </li></ul><ul><li>Due date of payment, ... </li></ul><ul><li>Insured risks, ... </li></ul><ul><li>Capital city, ... </li></ul><ul><li>Owner, ... </li></ul><ul><li>Construction cost, ... </li></ul>
  14. 14. Database = structured collection of digital data <ul><li>If not acquired in digital form, data need to be converted from analogue to digital form </li></ul><ul><li>Structuring is required to facilitate search and query of the data: </li></ul><ul><ul><li>Tables are often used to structure the data </li></ul></ul><ul><ul><li>Several software packages/tools exist to integrate data in tables for further processing </li></ul></ul><ul><ul><ul><li>MS-Access, MS-Excel, dBase, … are table- (row/column) based </li></ul></ul></ul><ul><li>Data collections contain very frequently an implicit indication of location: address, administrative/statistical unit, ... </li></ul>
  15. 15. From database to information system
  16. 16. From database to information system <ul><li>Data about entities : </li></ul><ul><li>persons </li></ul><ul><li>associations </li></ul><ul><li>companies </li></ul><ul><li>licences </li></ul><ul><li>invoices </li></ul><ul><li>municipalities, districts </li></ul><ul><li>properties, … </li></ul>What ? Wen ? What if ?
  17. 17. Information system <ul><li>Database equipped with tools which allow to ask questions and obtain answers </li></ul><ul><li>Information = structured and interpreted data, fit for specific use </li></ul><ul><li>Information = data put in its context to allow for interpretation </li></ul><ul><li>Information is derived from data using transformation tools </li></ul><ul><ul><li>query tools </li></ul></ul><ul><ul><li>computing tools </li></ul></ul><ul><ul><li>advanced analytical tools </li></ul></ul><ul><ul><li>presentation tools </li></ul></ul>
  18. 18. Questions about entities <ul><li>Persons </li></ul><ul><li>Associations </li></ul><ul><li>Companies </li></ul><ul><li>Invoices </li></ul><ul><li>Insurance polices </li></ul><ul><li>Provinces </li></ul><ul><li>Parcels </li></ul><ul><li>Buildings </li></ul><ul><li>… . </li></ul><ul><li>How old ? When 18 ? </li></ul><ul><li>How many members ? </li></ul><ul><li>Monthly salary cost ? </li></ul><ul><li>Amount unpaid ? </li></ul><ul><li>How large the risk ? </li></ul><ul><li>Budget deficit ? </li></ul><ul><li>(Un)built ? </li></ul><ul><li>For students ? </li></ul>What if taxes rise with 10% ? What deficit if #students decrease to 25.000 ?
  19. 19. From database to information system <ul><li>What ? </li></ul><ul><li>When ? </li></ul><ul><li>What if ? </li></ul><ul><li>WHERE ? </li></ul>
  20. 20. From maps and other collections of spatial data to GIS <ul><li>Data about spatial entities </li></ul><ul><li>rivers, hydrography </li></ul><ul><li>spatial destination zones </li></ul><ul><li>muncipalities </li></ul><ul><li>properties, buildings </li></ul><ul><li>... </li></ul>What ? When ? What if ? WHERE ?
  21. 21. Spatial entities (1) <ul><li>Cadastral entities, properties, buildings </li></ul><ul><ul><li>Patrimonium </li></ul></ul><ul><ul><li>Unbuilt parcels </li></ul></ul><ul><ul><li>Domicilies </li></ul></ul><ul><li>Entities related to spatial planning </li></ul><ul><ul><li>Transport infrastructure (road, railway, public transport connection, water- and airways,...) </li></ul></ul><ul><ul><li>Zones with a defined spatial destination </li></ul></ul><ul><ul><li>Zones with an effective land use </li></ul></ul><ul><ul><li>... </li></ul></ul>
  22. 22. Spatial entities (2) <ul><li>Entities related to security policy </li></ul><ul><ul><li>Location of traffic accidents </li></ul></ul><ul><ul><li>Properties where theft occurred </li></ul></ul><ul><ul><li>… </li></ul></ul><ul><li>Entities for planning of natural resources </li></ul><ul><ul><li>Fossil fuel fields </li></ul></ul><ul><ul><li>Mining zones </li></ul></ul><ul><ul><li>Fishing areas </li></ul></ul><ul><ul><li>Natural reserves </li></ul></ul><ul><ul><li>UNESCO world heritage </li></ul></ul>
  23. 23. Spatial entities (3) <ul><li>Entities related to agricultural and environmental policies </li></ul><ul><ul><li>Agricultural zones and parcels </li></ul></ul><ul><ul><li>Irrigation and drainage canals </li></ul></ul><ul><ul><li>Water abstraction points </li></ul></ul><ul><ul><li>Zones for soil erosion abatement </li></ul></ul><ul><li>Other entities </li></ul><ul><ul><li>Location of wind mills </li></ul></ul><ul><ul><li>Mangrove patches </li></ul></ul><ul><ul><li>Traffic lights </li></ul></ul><ul><ul><li>Sewer lines, electricity lines </li></ul></ul>
  24. 24. From data on spatial entities to spatial information <ul><li>From data regarding buildings, demography, migration to requirements for housing </li></ul><ul><li>From data regarding (non-) irrigated agricultural land, soils and climate to rice production capacity by province </li></ul><ul><li>From data on factories and owners of cars to air quality distribution </li></ul><ul><li>From data regarding beach resorts to regional touristic potential </li></ul>
  25. 25. Spatial entities and spatial objects <ul><li>Spatial entities </li></ul><ul><ul><li>Are elements of geographic reality with a clear boundary ‘crisp’ </li></ul></ul><ul><ul><li>Spatial entities of a given type are grouped into classes of spatial entities </li></ul></ul><ul><ul><li>Data about spatial entities can be implicitly spatial (adresses, other indirect references) or explicitly spatial (coordinates) </li></ul></ul><ul><li>Incorporation in a gDB of spatially explicit data about spatial entities requires abstraction and modelling </li></ul><ul><ul><li>Spatial entities are abstracted and modelled as spatial objects </li></ul></ul><ul><ul><li>‘ Feature’ is used as a synonym for both ‘entity’ and ‘object’ </li></ul></ul><ul><li>Spatial objects </li></ul><ul><ul><li>Spatial objects have: </li></ul></ul><ul><ul><ul><li>a location expressed according to a known reference system </li></ul></ul></ul><ul><ul><ul><li>A geometric shape: point, line, area/polygon, volume, one or more cells (pixel), voxel (3D-cells or cubes) </li></ul></ul></ul><ul><ul><ul><li>descriptive attributes (characteristics, properties, behaviour) </li></ul></ul></ul><ul><ul><li>Objects of the same shape-type and sharing the same attribute structure belong to one object class. Such class has most often more than one member </li></ul></ul>
  26. 26. An Example
  27. 27. Y X 6045 Identification Name 6045 Land Use        
  28. 28. Y X 101         Building 101 Name Identification
  29. 29. Y X A00233         99-nov-16t A00233 Date Identification
  30. 30. The real world = spatial entities + ??
  31. 31. Terrain <ul><li>Geographic reality is more than classes of spatial entities </li></ul><ul><li>The spatial continuum or Terrain in which entities occur </li></ul><ul><ul><li>Elevation (shaping relief and landscapes) </li></ul></ul><ul><ul><li>Depth of lakes, aquifers </li></ul></ul><ul><ul><li>Concentration of toxic substances in soil, surface water, … </li></ul></ul><ul><ul><li>Air quality </li></ul></ul><ul><ul><li>Noise, … </li></ul></ul><ul><li>Terrain = spatially variable characteristics of individual locations </li></ul><ul><li>Each terrain characteristic (e.g. elevation) is modelled as a Digitaal Terrain Model (DTM) of ‘single valued surface’ (surface) </li></ul>
  32. 32. From spatial database to GIS <ul><li>Data about spatial entities and/or terrain </li></ul><ul><li>rivers, hydrography </li></ul><ul><li>spatial destination zones </li></ul><ul><li>muncipalities </li></ul><ul><li>properties, buildings </li></ul><ul><li>elevation, bathymetry, … </li></ul>What ? When ? What if ? WHERE ?
  33. 33. gDB contains data about spatial entities and/or terrain <ul><li>All geographic data have three components: </li></ul><ul><ul><li>A geometric component: defines the position and shape of objects/locations with respect to a reference system; ALWAYS present </li></ul></ul><ul><ul><li>A descriptive component : attaches characteristics or attributes to objects or locations </li></ul></ul><ul><ul><li>Time as the third component. Locations and/or characteristics can change over time </li></ul></ul><ul><li>Geographic primitive = most elementary building block for the description of the geometric component of spatial entities and terrain </li></ul><ul><ul><li>Points </li></ul></ul><ul><ul><li>Cells </li></ul></ul>
  34. 34. Data in a gDB must be structured and interpreted <ul><li>Structuring of the geometric primitives ‘point’ or ‘cell’ </li></ul><ul><ul><li>into 2D-geographic objects : </li></ul></ul><ul><ul><ul><li>Elementary point, line, polygon objects </li></ul></ul></ul><ul><ul><ul><li>More complex network, region objects </li></ul></ul></ul><ul><ul><ul><li>Cells and aggregations of cells </li></ul></ul></ul><ul><ul><ul><li>Linked to ATTRIBUTE-information </li></ul></ul></ul><ul><ul><li>into 2.5D surfaces (for terrain characteristics): </li></ul></ul><ul><ul><ul><li>Relief, groundwater, noise </li></ul></ul></ul><ul><ul><li>into 3D-geographic objects (volumes) </li></ul></ul>
  35. 35. Example of geometric structuring Y X Points are structured into lines which define 2D-polygons
  36. 36. Example of geometric structuring Points/cells are structured into 2.5D surfaces
  37. 37. Data in a gDB must be structured and interpreted <ul><li>Interpretation of the geometric object- and surface structures through coupling with identification codes and characteristics: </li></ul><ul><ul><li>Object classes with individual members: specific parcels, water courses, land use zones, … </li></ul></ul><ul><ul><li>Surfaces which model specific terrain characteristics (e.g. digital elevation model; digital noise intensity model) </li></ul></ul>
  38. 38. Geographic databases <ul><li>Database = geographic database if it contains data about: </li></ul><ul><ul><li>Location </li></ul></ul><ul><ul><li>(Shape) </li></ul></ul><ul><ul><li>(Characteristics) of geographic objects and/or about terrain-characteristics </li></ul></ul><ul><li>gDB with computing and other functions = GIS </li></ul>
  39. 39. GI-Systems <ul><li>Are information systems; allow the user to formulate questions about geographic reality and obtain ‘best possible’ answers </li></ul><ul><li>Comparable to non-spatial information systems </li></ul><ul><li>Emphasis is on the geometric component, the ‘Where-question’ </li></ul>
  40. 40. Generic questions for a GIS <ul><ul><li>What is at a given location ? </li></ul></ul><ul><ul><ul><li>Which type of building ? How deep is the groundwater table ? </li></ul></ul></ul><ul><ul><li>Where are the entities with the specified characteristics ? </li></ul></ul><ul><ul><ul><li>Where are the severely degraded zones within the province ? </li></ul></ul></ul><ul><ul><li>What has changed since ? </li></ul></ul><ul><ul><ul><li>Which roads have been built since ? </li></ul></ul></ul><ul><ul><li>Which spatial patterns do occur ? </li></ul></ul><ul><ul><ul><li>Which is the configuration of atmospheric high and low pressure zones ? </li></ul></ul></ul><ul><ul><li>Which are the consequences of ? What if ? </li></ul></ul><ul><ul><ul><li>Which area will flood if a dike is perforated at a given location ? </li></ul></ul></ul>
  41. 41. GIS = IS GIS = TECHNOLOGY to build and exploit gDBs Spatial data modelling
  42. 42. GIS = IS GIS = TECHNOLOGY to build and exploit gDBs Management Transformation Visualisation, Query, Cartography Analysis
  43. 43. GIS as a technology <ul><li>Sets of computer programs, infrastructure and know-how to: </li></ul><ul><ul><li>A/D-convert </li></ul></ul><ul><ul><li>Structure </li></ul></ul><ul><ul><li>Process data about spatial entities and terrain into information </li></ul></ul><ul><ul><li>Query and communicate this information </li></ul></ul><ul><li>Based, to an important extent, on database-technology (DBMS) </li></ul><ul><li>Applicable in each thematic domain for which locations are important </li></ul><ul><li>Support of decisions </li></ul>
  44. 44. Summary of important items <ul><li>The world as it is or was; The world as we expect it or want it to be </li></ul><ul><li>Maps versus spatial databases </li></ul><ul><li>Spatial entities versus terrain characteristics </li></ul><ul><li>Nature of geographic information </li></ul><ul><li>A GIS is an information system </li></ul><ul><ul><li>that can provide answers to ‘where ?’ and related questions regarding the current, past, expected and planned geographic reality </li></ul></ul><ul><ul><li>that is based on a model of the geographic reality which is captured in a spatial database (gDB) </li></ul></ul><ul><li>GIS is a technology </li></ul><ul><ul><li>which enables to build and exploit spatial models/gDB </li></ul></ul>
  45. 45. Questions or remarks ? Thank you …

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