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Spatial Data Model

Spatial Data Model

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Spatial Data Model

  1. 1. DEPARTMENT OF GEOGRAPHY AND ENVIRONMENT UNIVERSITY OF DHAKA
  2. 2. Spatial data are often referred to as coverages, or layers Depending on the type of features they represent, and the purpose to which the data will be applied, layers will be one of 2 major types: Vector data represent features as discrete points, lines, and polygons Raster data represent the landscape as a rectangular matrix of square cells
  3. 3. The 2 basic data structures in any fully-functional GIS are: Vector, e.g., ◦ArcInfo Coverages ◦ArcGIS Shape Files ◦CAD ◦GBF ◦TIGER etc. Raster, e.g., ◦ArcInfo Grids ◦Images ◦Digital Elevation Models (DEMs) ◦PNG ◦JPEG etc.
  4. 4. Vector data are composed of: points, lines, and polygons Points represent discrete locations on the ground. Each layer is a combination of the coordinate (vector) data, and an attribute table containing a record for each vector feature.
  5. 5. Lines represent linear features, such as rivers, roads and transmission cables.
  6. 6. Arcs are composed of nodes and vertices. Arcs begin and end at nodes, and may have 0 or more vertices between the nodes. The vertices define the shape of the arc along its length. Arcs which connect to each other will share a common node.
  7. 7. In ArcGIS there are 3 major types of vector data source files: ESRI geodatabases ESRI shape files ArcInfo coverages ESRI geodatabases are a relatively new format. A geodatabase stores all features and related tables, as well as other files, within a single or distributed database format. A single shapefile represents features that are either point, line, or polygon in spatial data type.
  8. 8. For each shapefile there exist at least 3 files: The shape data (stored in the .shp file) An associated dBASE (relational database) table (stored in the .dbf file) And a spatial index (stored in the .shx file). ArcInfo Coverages are a basic implementation of the vector arc-node topological model The coverage can be a multi-feature dataset, composed of polygons, arcs, nodes, label points, and tics.
  9. 9. Raster datasets are composed of rectangular arrays of regularly spaced square grid cells.
  10. 10. Run-length Encoding Quadtree
  11. 11. Total Marks: 15 Time: 40 minutes Q 1: What is meant by ‘Geodatabase’? What are the components of a geodatabase? Design a geodatabase to map the administrative units of Bangladesh. (10) Q 2: Define georeferencing. Identify the essence of performing georeference. (05)

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