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Something basic about GIS

Something basic about GIS. Ming-Chun Lee. What is GIS ?. GIS = Geographic Information System Three components: Geography – the real world Information – data and information Systems – technologies. A Definition of GIS. GIS = Geographic Information System Worboys, 1995:

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Something basic about GIS

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  1. Something basic about GIS Ming-Chun Lee

  2. What is GIS ? • GIS = Geographic Information System • Three components: • Geography – the real world • Information – data and information • Systems – technologies

  3. A Definition of GIS • GIS = Geographic Information System • Worboys, 1995: • A Geographic Information System (GIS) is a computer-based information system that enables one to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information.

  4. Functions of GIS • Data Collection • Storage & Management • Retrieval • Conversion • Analysis • Display

  5. Applications of GIS • How GIS can be used: • Infrastructure Management • Transportation Network Routing • Floodplain Management • Emergency Response Planning • Noise Pollution Analysis • Participatory Planning Processes • Jobs/Housing Spatial Balance • and more …

  6. Administrative Boundaries Utilities Zoning Buildings Parcels Hydrography Streets Digital Orthophoto The GIS Data Model • Data Organized by Layers/Themes

  7. GIS Database • GIS data is organized by Layers/Themes • A Theme is a collection of geographic features (usually a separate file), such as boundaries, roads, together with the attributes (may stored in other files) of those features • A set of Themes for a geographic area makes up a GIS Database (a group of files)

  8. The GIS Data Model • Layers Integrate Using Explicit Location on the Earth’s Surface • Themes have to be georeferenced.

  9. Georeferencing • Identifying Locations on the Earth Using Locations on a Map or GIS • Aspects of Georeferencing • Coordinate Systems • Geographic Coordinate System • Projected Coordinate System • Projections

  10. Coordinate Systems • A Method of Locating Objects on the Earth’s Surface • Examples: • Geographic (Global) Coordinate System • Projected (Cartesian) Coordinate System

  11. Geographic Coordinate System • Geographic Coordinate System (GCS) uses a three dimensionalspherical surface to define locations on the earth.

  12. Geographic Coordinate System • In the spherical system, horizontal lines are lines of equal latitude, or parallels • Vertical lines are lines of equal longitude, or meridians. • These lines encompass the globe and form a gridded network called a graticule

  13. Geographic Coordinate System A point is referenced by its longitudeand latitudevalues. Longitude and latitude are angles measured from the earth’s center to a point on the earth’s surface. The angles often are measured in degrees (or in grads).

  14. Measuring Latitude • Latitude Measures the Angular Distance from the Equator North Pole(90 º N) 60 º N 60 º Equator South Pole(90 º S) Side View

  15. Measuring Longitude 135 º E • Longitude Measures the Angular Distance from the Prime Meridian (Greenwich, UK) North Pole Equator 135 º 70 º 70 º W Prime Meridian (0 º) Top View

  16. Projected Coordinate Systems • A projected coordinate system is defined on a flat,two-dimensionalsurface. • A projected coordinate system is alwaysbased on ageographic coordinate system that isbased on a sphere or spheroid. • In a projected coordinate system, locations areidentified by x,y coordinates on a grid

  17. Projection • Whether you treat the earth as a sphere or aspheroid, you must transform its three-dimensionalsurface to create a flat map sheet. • The Process of Systematically Transforming Positions on the Earth’s Spherical Surface to a Flat Map While Maintaining Spatial Relationships

  18. Geometric Models for Projection • Conical • Tangent along a Specific Latitude • Screen is a conic surface. Lamp at the center of the earth • Cylindrical • Tangent along Equator or a Longitude • Screen is a cylindrical surface. Lamp at the center of the earth • Planar/Azimuthal/Zenithal • Tangent at a Single Point • Screen is a flat surface tangent to the earth. Lamp at various positions

  19. Map Projection and Distortion • For Geometric Properties Affected by Projection: • Shape or Angle • Area • Distance • Direction • All projections produce some distortion

  20. Common Projection Systems • Universal Transverse Mercator (UTM) • State Plane (SP)

  21. Universal Transverse Mercator • Series of Cylindrical Projections, Tangential to a Longitude Line • 60 Zones, One Every 6 Degrees Longitude • Each Zone: • Width is 6º in Longitude • Height is from 80º S to 84º N in Latitude

  22. State Plane • Planar Projection • Tangent at Different Points for Each State • Most States Have Two or More Zones

  23. Types of GIS Data • Describes Objects In Terms Of: • Spatial Data • Absolute X,Y Coordinates – Locations • Size, and Shape • Attributes • Characteristics associated with Geography

  24. GIS Associates Spatial and Attribute Data in a Geo-Referenced Database ARC INFO 1 3 ID AREA PERIM CLASS LANDUSE 1 260210 20688 100 Single Family 2 18210 20688 100 Multi Family 3 260210 20688 100 Commercial 4 258876 16880 200 Forest 5 3008 88 500 Water 5 2 4

  25. Data models • Data models: Formats in which geographic data is stored and managed. • Vector Data Models (Features) • Points • Lines • Polygons • Raster Data Models (Surfaces)

  26. Raster and Vector Data Models point line polygon Raster Representation Vector Representation

  27. Raster Data Models • Raster Data Model • Location is referenced by a grid cell in a rectangular array or matrix • Attribute is represented as a single value for that grid cell

  28. Raster Data Models

  29. Raster Data Models • Raster Data Model • Typical data sources: • Images from remote sensing (LANDSAT, SPOT) • Elevation data from USGS • Best for continuous data: • Elevation • Temperature

  30. Raster Data Model Uses • Elevation • Temperature • Noise Levels • Air Quality • Distance or Accessibility Surfaces • Probabilities (e.g. flooding, liquefaction) • Photographic Images

  31. Vector Data Models • Vector Data Model • Location is referenced by x,y coordinates, which can be linked to form lines and polygons • Attributes referenced through unique ID number to tables

  32. Features • Geographic objects that have different shapes are represented as features

  33. Features • Points are a pair of x,y coordinates

  34. Features • Lines are sets of coordinates that define a shape

  35. Features • Polygons are sets of coordinates defining boundaries that enclose areas.

  36. Vector Data Models • Vector Data Model • Typical data sources: • DIME (Dual Independent Map Encoding) and TIGER (Topologically Integrated Geographic Encoding and Referencing file) files from US Census • DLG (Digital Line Graph)from USGS for streams, roads, etc. • Best for features with discrete boundaries: • Soil Type • Land Use

  37. Vector Data Model Uses • Land Use or Zoning Classifications • Polygons • Transportation Networks • Points and Polylines • Hydrology • Polylines for Rivers, Polygons for Water Bodies • Utilities • Points for Facilities, Polylines for Pipelines & Wires

  38. Raster Advantages & Disadvantages • Raster Disadvantages • Spatial Inaccuracies Common • Low Resolution, Relative to Vector Data • Imprecise Locational Data • Requires All Cells to be Coded • Not As Efficient for Discrete Data or Features • Raster Advantages • Easy to Understand the Data Model • Easy to Analyze • Low Computing Requirements • Compatible with Remote Sensing Sources • Efficient for Continuous Data • Easy to Use in Modeling

  39. Vector Advantages & Disadvantages • Vector Disadvantages • Difficult to Manage Data Storage • High Computing Requirements • Complex to Perform Overlay and Modeling Operations • Inefficient for Continuous Data • Vector Advantages • More Readable as a Map • Higher Resolution than Raster Data • Can Have High Spatial Accuracy • Can Have Storage Advantages • Can Be Topological • Efficient for Discrete Data or Features

  40. Introduction to ArcGIS • ArcGIS is a software program , used to create, display and analyze geospatial data , developed by Environmental Systems Research Institute (ESRI) of Redlands, California. • http://www.esri.com/

  41. ESRI’s ArcGIS Platform • Suite of Three Integrated Applications: • ArcCatalog • ArcMap • ArcToolbox

  42. Components of ArcGIS • ArcCatalog is used for browsing for maps and spatial data and managing spatial data, viewing and creating metadata. • ArcMap is used for visualizing spatial data, performing spatial analysis and creating maps to show the results. • ArcToolboxis an interface for accessing the data conversion and analysis function that come with ArcGIS.

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