Spatial Data Model
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The document discusses different types of spatial data used in geographic information systems (GIS). It describes vector data, which represents geographic features as points, lines, and polygons, and raster data, which divides the landscape into a grid of cells. It outlines some common vector data formats like shapefiles, coverages, and geodatabases, and raster formats like grids and digital elevation models. It provides details on how vector data structures represent points, lines, polygons, and their topological relationships in ArcGIS.
Spatial Data Model
- 1. DEPARTMENT OF GEOGRAPHY AND ENVIRONMENT UNIVERSITY OF DHAKA
- 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. 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. 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.
- 6. Lines represent linear features, such as rivers, roads and transmission cables.
- 7. 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.
- 8. 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.
- 9. 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.
- 10. Raster datasets are composed of rectangular arrays of regularly spaced square grid cells.
- 15. 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)