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Basic of gis concept and theories

Geographical information systems (GIS)

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Basic of gis concept and theories

  2. 2. Remote Sensing (RS) Remotely sensing the useful information of object (earth) Process of recording, measuring and interpreting imagery and digital representations of energy patterns derived from noncontact sensor systems Geographic Information System (GIS) A system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data Application of Remote Sensing and Geographical Information System in Civil Engineering 2
  3. 3. • G (Geography) - a particular form of Information System applied to geographical data (location, co-ordinates, maps etc..) • I (Information) S (System) is a set of processes, executed on raw data, to produce information which will be useful in decision-making • A series of steps from observation and collection of data through analysis to information (Data Handling) • The DATA into INFORMATION PATHWAY ( Data = Facts; Information = Facts with Meaning) Basic definition of GIS 3
  4. 4. • GIS as a Toolbox • Usage of GIS for Mapping • Static vs. Interactive Maps • GIS as Interactive Cartography • The Analysis Distinction - Query to Analysis • • GIS as an Approach to Science • GIS as a Discipline Basic Usage of GIS 4
  5. 5. Origin of GIS Computer Aided Cartography (CAC) Remote Sensing (RS) Computer Aided Design/ Drafting (CAD) Database Management Systems (DBMS) GIS Integrated Technologies 5
  6. 6. Geographic Information System (GIS) 6
  7. 7. GISs are simultaneously the telescope, the microscope, the computer, and the Xerox machine of regional analysis and synthesis of spatial data. (Ron Abler, 1988) “A powerful set of tools for storing and retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes“ (Burrough, 1986, p. 6). “Automated systems for the capture, storage, retrieval, analysis, and display of spatial data." (Clarke, 1995, p. 13). "An information system that is designed to work with data referenced by spatial or geographic coordinates. In other words, a GIS is both a database system with specific capabilities for spatially-referenced data, as well as a set of operations for working with the data" (Star and Estes, 1990, p. 2). "A geographic information system is a special case of information systems where the database consists of observations on spatially distributed features, activities or events, which are definable in space as points, lines, or areas. A geographic information system manipulates data about these points, lines, and areas to retrieve data for ad hoc queries and analyses" (Dueker, 1979, p 106). What Is GIS - a Brief Introduction 7
  8. 8. What Is GIS - a Brief Introduction Different mapping systems: Electronic atlases Thematic mapping systems Street-based mapping systems GIS: all these things + much more analysis, import/export, combination of different data, dynamic map update, etc “A system of hardware, software, data, people, organizations and institutional arrangements for collecting, storing, analyzing, and disseminating information about areas of the earth (Dueker and Kjerne, 1989) Use of geography to integrate information from different sources 8
  9. 9. Information Remote sensing data Geographic data Hardware Computer Digitizer Scanner Printer/Plotter Tools for GIS 9 Software Desktop GIS Internet GIS CAD Software Database Software Multimedia (photos, videos, 3D models) Geographic data – 80% of government data collected is associated with some location in space Information - attributes, or the characteristics (data), can be used to symbolize and provide further insight into a given location System – a seamless operation linking the information to the geography – which requires hardware, networks, software, data, and operational procedures …not just software! …not just for making maps!
  10. 10. 10 GIS Functional Elements 1. Acquisition digitizing, editing, topology building, projection transformation, format conversion, attribute assignment etc. 2. Pre-Processing Analogue to digital Conversion of units 3. Management Data archival, databases (hierarchical model, networking model, relational databases etc.) 4. Manipulation and Analysis Buffering, overlay, connectivity operations etc. 5. Output (Product Generation) Thematic maps, 3D birds eye view, scaled maps etc 10
  11. 11. 11 Why a GIS Old Records/maps are poorly maintained Poorly Updated Inaccurate No Sharing No data retrieval service for maps 11
  12. 12. 12 Benefits of GIS Once a GIS is implemented, following benefits are expected: Better Maintained data Standard format Easy revision, Easy updation Easy Units conversion Easy to share Easier to search, analyze and represent Many value added products Enhance productivity of staff Time and Money saved Better Decision making 12
  13. 13. 13 GIS as a Multi-Disciplinary Science Combination of following traditional sciences Geography Statistics Cartography Remote Sensing Photogrammetry Computer Science Operation Research Mathematics Surveying Civil Engineering Geodesy Urban Planning Environmental Engineering, etc. 13
  14. 14. 14 Alternate Names of GIS Land Information System (LIS) AM/FM-Automated Mapping and Facilities Management Environmental Information System (EIS) Resource Information System (RIS) GIS Is now becoming independent DISCIPLINE in the name of GEOINFORMATICS, or GEOSPATIAL INFORMATION SYSTEM. 14
  15. 15. 15 Areas of GIS Applications Facilities Management e.g. PTCL, SNGPL, Irrigation, WASA, for: locating underground pipes and cables) Environmental and Natural Resource management suitable lands for crops, management of forests, EIA, Disaster Management etc. Street Network Car Navigation, locating houses and streets, rescue services etc. Planning and Engineering DAMS, Power Projects, urban planning, regional planning Land Information System Board of Revenue, taxation, zoning, land acquisition. 15
  16. 16. 16 GIS and DSS GIS is usually an important component of modern Decision Support Systems (DSS) DSS components: Data Base Statistical Analysis Numerical Model Input and output facility 16
  17. 17. 17 USE OF GIS as DSS Driving Forces: Population, Health, Wealth, Technology, Politics, Economic Analysis and Assessment by GIS Decision Making: Planning and Management Human Impacts: Development, Urbanization, Industrialization, Construction, Energy Use Environmental Change: Land use Change, Change of Life Style, Land Degradation, Pollution, Climate Change Monitoring By Remote Sensing 17
  18. 18. 18 GIS Software ESRI: ARC/INFO, ARC VIEW, ARC GIS Intergraph: MGE Grass Information Centre: GRASS* Clark University: IDRISI AUTODESK: ARC MAP ILWIS: Integrated Land and Water Information System. 18
  19. 19. Advantages of GIS Exploring both geographical and thematic components of data in a holistic way Stresses geographical aspects of a research question Allows handling and exploration of large volumes of data Allows integration of data from widely disparate sources Allows analysis of data to explicitly incorporate location Allows a wide variety of forms of visualisation Limitations of GIS Data are expensive Learning curve on GIS software can be long Shows spatial relationships but does not provide absolute solutions Origins in the Earth sciences and computer science. Solutions may not be appropriate for humanities research Advantages and Disadvantages of GIS 19
  20. 20. Basics of GIS Lets starts 20
  21. 21. Basic Geographical Concepts 21 One of the most common products of a GIS is a map Global to local Spatial Objects Points Line/ node Polygon /chain
  22. 22. 22 Basic Geographical Concepts Spatial Object: Delimited Geographical areas, with a number of different kind of associated attributes Point: A spatial object with no area. A key attribute is its geodetic location. Many Attributes can be associated with a Point Line: A spatial object, made up of a connected sequence of points. Lines have no width, thus a specified location will be on one side of a line or other, but never on a line. Nodes: Special kinds of points showing start, end and junction of line segments. Polygon: A closed Area. Simple Polygons are undivided areas, while complex polygons are divided into areas of different characteristics. Chains: Special kinds of line segments, which corresponds to a portion of the bounding edge of polygon. 22
  23. 23. Basic Geographical Concepts Parcels: The allotment of some amount by dividing something 23
  24. 24. 24 Scale Ratio of distance on map (or image) to their true length on the earth’s surface Large Scale: A scale is relatively large, if the area or length represented on map (or image) is large Small Scale: A scale is relatively small, if the area or length represented on map (or image) is small e.g. 1:10,000 is large scale as compared to 1:100,000. Resolution Refers to minimum size of the element which we can distinguish on a map. For Raster Maps, it is size of cell For Maps, it is = (Area/No of elements)^0.5 Higher the resolution, more information are available. RESEL=Resolution Element Basic Geographical Concepts 24
  25. 25. Basic Geographical Concepts 25
  26. 26. 26 Attributes Pertinent (important) information of geospatial data. e.g. if a line is representing a road through geographic data (Lat., Long. or Easting , Northing), then its helping information such as width, condition, name, metaled or un-metaled etc. are its attributes. Only those attributes should be selected/acquired which might be required in the analysis. Basic Geographical Concepts 26
  27. 27. A GIS stores information about the world as a collection of thematic layers that can be linked together by geography The basic data type in a GIS reflects traditional data found on a map Spatial data describes the absolute and relative location of geographic features. Attribute data describes characteristics of the spatial features. These characteristics can be quantitative and/or qualitative in nature. Attribute data is often referred to as tabular data. GIS data model (Database management systems-DBMS ) 27
  28. 28. Three basic types of spatial data models have evolved for storing geographic data digitally. These are referred to as: Raster; Vector; Image. SPATIAL DATA MODELS Image data utilizes techniques very similar to raster data, however typically lacks the internal formats required for analysis and modeling of the data 28
  29. 29. Raster data models incorporate the use of a grid-cell data structure where the geographic area is divided into cells identified by row and column. For digital representations of aerial photographs, satellite images, scanned paper maps, and other applications with very detailed images. Raster data models A raster data structure is in fact a matrix where any coordinate can be quickly calculated if the origin point is known, and the size of the grid cells is known 29
  30. 30. Vector storage implies the use of vectors (directional lines) to represent a geographic feature. Vector data is characterized by the use of sequential points or vertices to define a linear segment. Each vertex consists of an X coordinate and a Y coordinate. Vector lines are often referred to as arcs and consist of a string of vertices terminated by a node. Vector Data models 30
  31. 31. Geometry and Topology of Vector data 31 Topology is a mathematical concept that has its basis in the principles of feature adjacency and connectivity The most popular method of retaining spatial relationships among features is to explicitly record adjacency information in what is known as the topologic data model The topologic data structure is often referred to as an intelligent data structure
  32. 32. Image data is typically used in GIS systems as background display data (if the image has been rectified and georeferenced); or as a graphic attribute Image data must be converted into a raster format (and perhaps vector) to be used analytically with the GIS Image Data models 32
  33. 33. Attribute data refers to pertinent information attached to each geo-spatial data. A variety of different database models exist for the storage and management of attribute data. The most common are: 1. Tabular (Outdates in GIS !), 2. Hierarchial 3. Network 3. Relational 5. Object Oriented The hierarchical database organizes data in a tree structure. Data is structured downward in a hierarchy of tables. The network database organizes data in a network or plex structure. Any column in a plex structure can be linked to any other The object-oriented database model manages data through objects. An object is a collection of data elements and operations that together are considered a single entity. The object-oriented database is a relatively new model. This approach has the attraction that querying is very natural, as features can be bundled together with attributes at the database administrator's discretion. Attribute data models 33
  34. 34. A separate data model is used to store and maintain attribute data for GIS software. These data models may exist internally within the GIS software, or may be reflected in external commercial Database Management Software (DBMS) Note
  35. 35. Attribute database models Examples of object- oriented data model Hierarchial and network database models have not gained any noticeable acceptance for use within GIS 35
  36. 36. A relational database organizes data in tables. Each table, is identified by a unique table name, and is organized by rows and columns. Each column within a table also has a unique name. Attribute data models UNIQUE STAND NUMBER DOMINANT COVER GROUP AVG. TREE HEIGHT STAND SITE INDEX STAND AGE 001 DEC 3 G 100 002 DEC-CON 4 M 80 003 DEC-CON 4 M 60 004 CON 4 G 120 The relational database model is the most widely accepted for managing the attributes of geographic data. 36
  37. 37. Basic linkages between a vector spatial data (topologic model) and attributes maintained in a relational database file (From Berry) Relational Attribute model 37
  38. 38. Attribute data consists of qualitative or quantitative data. Qualitative data specify the types of object, while quantitative data can be categorized into ratio data, data measured in relation to a zero starting point; interval data, data arranged into classes; and ordinal data, which specify quality by using text. Relational Attribute model 38
  39. 39. ‘Which is best? depends in 4 issues coordinate precision speed of analytical processing mass storage requirements characteristics of phenomena Choice between raster and vector data Choice between raster and vector data 39
  40. 40. Data on different themes are stored in separate “layers” As each layer is geo-referenced layers from different sources can easily be integrated using location This can be used to build up complex models of the real world from widely disparate sources Spatial Data Layers (layers) The definition of data layers is fully dependent on the area of interest and the priority needs of the GIS. Layer definitions can vary greatly depending on the intended needs of the GIS 40
  41. 41. As data acquisition or data input of geospatial data in digital format is most expensive (about 80% of the total GIS project cost) and procedures are time consuming in GIS Required Data Sources for GIS 41
  42. 42. The geographic location of each cell is implied by its position in the cell matrix. Accordingly, other than an origin point, e.g. bottom left corner, no geographic coordinates are stored. Due to the nature of the data storage technique data analysis is usually easy to program and quick to perform. The inherent nature of raster maps, e.g. one attribute maps, is ideally suited for mathematical modeling and quantitative analysis. Discrete data, e.g. forestry stands, is accommodated equally well as continuous data, e.g. elevation data, and facilitates the integrating of the two data types. Grid-cell systems are very compatible with raster-based output devices, e.g. electrostatic plotters, graphic terminals. Advantages of Raster data 42
  43. 43. The cell size determines the resolution at which the data is represented.; It is especially difficult to adequately represent linear features depending on the cell resolution. Accordingly, network linkages are difficult to establish. Processing of associated attribute data may be cumbersome if large amounts of data exists. Raster maps inherently reflect only one attribute or characteristic for an area. Since most input data is in vector form, data must undergo vector-to-raster conversion. Besides increased processing requirements this may introduce data integrity concerns due to generalization and choice of inappropriate cell size. Most output maps from grid-cell systems do not conform to high-quality cartographic needs. Disadvantages of Raster data 43
  44. 44. Data can be represented at its original resolution and form without generalization. Graphic output is usually more aesthetically pleasing (traditional cartographic representation); Since most data, e.g. hard copy maps, is in vector form no data conversion is required. Accurate geographic location of data is maintained. Allows for efficient encoding of topology, and as a result more efficient operations that require topological information, e.g. proximity, network analysis. Advantages of Vector data 44
  45. 45. The location of each vertex needs to be stored explicitly. For effective analysis, vector data must be converted into a topological structure. This is often processing intensive and usually requires extensive data cleaning. As well, topology is static, and any updating or editing of the vector data requires re-building of the topology. Algorithms for manipulative and analysis functions are complex and may be processing intensive. Often, this inherently limits the functionality for large data sets, e.g. a large number of features. Continuous data, such as elevation data, is not effectively represented in vector form. Usually substantial data generalization or interpolation is required for these data layers. Spatial analysis and filtering within polygons is impossible Disadvantages of Vector data 45
  46. 46. Comparison b/w raster and vector data 46
  47. 47. Assignment 47
  48. 48. Comments…. Questions…. Suggestions…. 48 I am greatly thankful to all the information sources (regarding remote sensing and GIS) on internet that I accessed and utilized for the preparation of present lecture. Thank you !