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Introduction to basic concepts on Geographical Information Systems

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 Gis Concepts 1/5 Presentation Transcript

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