1 / 56

Last week

Geographic Information Systems: an introduction Week III Data models cont’d The Nature of Geographic Data. Last week. Representing geographic data E.g. continuous fields, discrete objects Data models E.g. Raster, vector. Data Model Levels. Reality. Human-oriented. Conceptual Model.

gabby
Download Presentation

Last week

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Geographic Information Systems:an introductionWeek IIIData models cont’dThe Nature of Geographic Data

  2. Last week • Representing geographic data • E.g. continuous fields, discrete objects • Data models • E.g. Raster, vector

  3. Data Model Levels Reality Human-oriented Conceptual Model Increasing Abstraction Logical Model Computer-oriented Physical Model

  4. CAD Graphical Image Raster TIN Geo-relational Object Engineering design Simple mapping Image processing and analysis Spatial analysis / modeling Surface /terrain analysis / modeling Geoprocessing geometric features Features with behavior Logical Data Models & Applications

  5. Raster and Vector Models • Raster – implementation of field conceptual model • Array of cells used to represent objects • Useful as background maps and for spatial analysis • Vector – implementation of discrete object conceptual model • Point, line and polygon representations • Widely used in cartography, and network analysis

  6. Rasters and Vectors • How to represent phenomena conceived as fields or discrete objects? • Raster • Divide the world into square cells • Register the corners to the Earth • Represent discrete objects as collections of one or more cells • Represent fields by assigning attribute values to cells • More commonly used to represent fields than discrete objects

  7. Legend Mixed conifer Douglas fir Oak savannah Grassland Raster representation. Each color represents a different value of a nominal-scale field denoting land cover class.

  8. Characteristics of Rasters • Pixel size • The size of the cell or picture element, defining the level of spatial detail • All variation within pixels is lost • Assignment scheme • The value of a cell may be an average over the cell, or a total within the cell, or the commonest value in the cell • It may also be the value found at the cell’s central point

  9. Vector Data • Used to represent points, lines, and areas • All are represented using coordinates • One per point • Areas as polygons • Straight lines between points, connecting back to the start • Point locations recorded as coordinates • Lines as polylines • Straight lines between points

  10. Vector Data .ancaster POINTS POINTS POLYGON POLYGON LINES LINES Millbrook Lane ANNOTATION ANNOTATION NODES NODES

  11. Vector - Land Records Surveyed feature 20.37’ 26.23’ R 10’ 45.81’ 45.81’ 13 12 35.44’ 30.5’ 26.23’ GIS Link Survey / / / Survey point / 9 / / Computation

  12. Raster vs Vector • Volume of data • Raster becomes more voluminous as cell size decreases • Raster is vaster • Source of data • Remote sensing, elevation data come in raster form • Vector favored for administrative data • Vector is more appropriate when storing large amounts of attribute information. • Software • Some GIS better suited to raster, some to vector

  13. Data Model Levels Reality Human-oriented Conceptual Model Increasing Abstraction Logical Model Computer-oriented Physical Model

  14. Data Models and Spatial Analysis • Raster v. vector? • Picture of a large burn • Picture of an urban landscape • Picture of burning houses • Map of burning houses

  15. Geo-relational Model

  16. Formats of feature data models in ArcGIS • Georelational models • Coverages • Shapefiles • Database Management System (DBMS) • Geodatabase

  17. Coverages Traditional model for complex (multiple feature types) geoprocessing environments

  18. Coverages . primary composite secondary routes sections regions annotation ticks links

  19. Shapefiles Simple, open, “flatfile” based format for single data features

  20. Geodatabase Object-based data model where all features are contained in database; features can exhibit “behavior”

  21. Compression techniques No compression Run length encoding (lossless)

  22. ADRG - National Imagery and Mapping Agency (NIMA)'s ARC Digitized Raster Graphics BIL - Band Interleaved by Line (image format linked with satellite derived imagery) CADRG - National Imagery and Mapping Agency (NIMA)'s Compressed ARC Digitised Raster Graphics (nominal compression of 55:1 over ADRG) CIB - National Imagery and Mapping Agency (NIMA)'s Controlled Image Base (type of Raster Product Format) Digital raster graphic (DRG) - digital scan of a paper USGStopographic map ECW - Enhanced Compressed Wavelet (from ERMapper). A compressed wavelet format, often lossy. ESRI grid - binary and ASCII raster formats used by ESRI GeoTIFF - TIFF variant enriched with GIS relevant metadata IMG - ERDAS IMAGINE image file format MrSID - Multi-Resolution Seamless Image Database (by Lizardtech). A compressed wavelet format, often lossy.

  23. Vector formats Geography Markup Language (GML) - XML based open standard (by OpenGIS) for GIS data exchange DXF - Contour elevation plots in AutoCAD DXF format Shapefile - ESRI's open, hybrid vector data format using SHP, SHX and DBF files Simple Features - Open Geospatial Consortium specification for vector data MapInfo TAB format - MapInfo's vector data format using TAB, DAT, ID and MAP files National Transfer Format (NTF) - National Transfer Format (mostly used by the UK Ordnance Survey) TIGER - Topologically Integrated Geographic Encoding and Referencing Vector Product Format - National Imagery and Mapping Agency (NIMA)'s format of vectored data for large geographic databases. GeoMedia - Intergraph's MicrosoftAccess based format for spatial vector storage. ISFC - Intergraph's Microstation based CAD solution attaching vector elements to a relational MicrosoftAccess database Personal Geodatabase - ESRI's closed, integrated vector data storage strategy using Microsoft's AccessMDB format Coverage - ESRI's closed, hybrid vector data storage strategy. Legacy ArcGIS Workstation / ArcInfo format with reduced support in ArcGIS Desktop lineup

  24. Grid formats (for elevation) USGS DEM - The USGS' Digital Elevation Model DTED - National Imagery and Mapping Agency (NIMA)'s Digital Terrain Elevation Data GTOPO30 - Large complete Earth elevation model at 30 arc seconds SDTS - The USGS' successor to DEM Other formats Binary Terrain - The Virtual Terrain Project's Binary Terrain format Well-known text (WKT) – ASCII spatial projection description (ESRI uses a *.prj extension) Well-known binary (WKB) - Binary spatial projection description

  25. Geo-relational Model

  26. Formats of feature data models in ArcGIS • Georelational models • Coverages • Shapefiles • Object model • Geodatabase

  27. Coverages Traditional model for complex geoprocessing environments primary composite secondary • Topologically correct • Data processing and spatial analysis • Complex data structure • Difficult interchange (E00) • Multiple feature types . routes sections regions annotation ticks links

  28. Coverages

  29. Shapefiles Simple, open, “flatfile” based format for single data features • Single feature type within one file • No topology • Easy to transport • Open

  30. Shapefiles

  31. Geodatabase Object-based data model where all features are contained in database; features can exhibit “behavior” • Multiple features stored as tables • Data processing topology • Object oriented instead of restricted to points, lines, polys • Resides in traditional database

  32. Geodatabase

  33. Topology • Field within mathematics. • The study of the general abstract nature of continuity or "closeness" on spaces. • System administrators actually describe computer networks as being topologic • Bus topology • Ring topology • Star topology • Leonhard Euler • The solution of a problem relating to the geometry of position 1736. • Euler was aware that he was dealing with a different type of geometry where distance was not relevant.

  34. Consider the problem of building a fusion reactor which confines a plasma by a magnetic field.

  35. The solution of a problem relating to the geometry of position

  36. Topology • Science and mathematics of geometric relationships • Simple features + topological rules • Connectivity • Adjacency • Shared nodes / edges • Topology uses • Data validation • Spatial analysis (e.g. network tracing, polygon adjacency)

  37. Topology and GIS • Topology in GIS is generally defined as the spatial relationships between adjacent or neighboring features. • Two types of topology: • Polygon topology • Line topology • three advantages of incorporating topology in GIS databases:data management, data correction and spatial analysis

  38. Data correction and storage

More Related