Geographic Information Systems

1. Geographic Information Systems Vector and Raster Data Models

2. Raster • exhaustive regular or irregular partitioning of space • associated with the field view • location-based • Vector • points, lines, polygons • associated with the object view • object-based Spatial Data Models

3. Spatial Data Models

4. Each point, line, or polygon is stored as a record in a file that consists of that entity’s ID and a list of coordinates that define geometry. Spaghetti Vector Data Model For Points: • ID Coordinates • 3,4 • 5,5 2 1

5. Each point, line, or polygon is stored as a record in a file that consists of that entity’s ID and a list of coordinates that define geometry. Spaghetti Vector Data Model For Lines: • ID Coordinates • (0,1), (3,4), (5,6) • (3,1), (5,2), (4,3) 1 2

6. Each point, line, or polygon is stored as a record in a file that consists of that entity’s ID and a list of coordinates that define geometry. Spaghetti Vector Data Model For Polygons: • ID Coordinates • (2,4), (4,3), (3,6) , (2,4), • (3,1), (5,2), (4,3), (3,2), (3,1) 1 2

7. Advantages • simple • efficient for display and plotting • Disadvantages • inefficient for most types of spatial analysis Spaghetti Vector Data Model

8. Composed of points, lines, and polygons • Node: a point at the intersection of three or more lines • In addition to coordinate locations, the topologic relationships among geometric features are explicitly recorded Vector Topologic Data Model

9. Arc Coordinate Data Arc StartXY IntermediateXY EndXY a1 4,5 (4,8), (8,8), (8,1), (4,1) 4,3 a2 4,5 (6,7), (6,3) 4,3 a3 4,5 (1,3) 4,3 a4 4,3 4,5 A n1 B a2 a1 a3 a4 C n2 Polygon Topology Arc Topology Node Topology Arc Start End Left Right a1 n1 n2 A a2 n1 n2 A B a3 n1 n2 C a4 n2 n1 C B ID Arcs A a1, a2 B a2, a4 C a3, a4 Node Arcs n1 a4, a2, a1, a3 n2 a2, a4, a3, a1 Vector Topologic Data Model

10. Planar Enforcement: • No two individual features can overlap. • There are no ‘holes’ or ‘íslands’ that are not themselves features. • Every feature is represented as a record in the attribute table. Vector Topologic Data Model

11. Spaghetti: can encode as 2 or 3 polygons (and have 2 or 3 records in the attribute table) Topologic: must be encoded as 3 polygons (and have 3 records in the attribute table) Vector Topologic vs. Spaghetti

13. Triangulated Irregular Network (TIN)

14. Triangulated Irregular Network (TIN)

15. Hybrid Approach:stores spatial data and attribute data in different data models (typically relational data model for attribute data and proprietary data structure for spatial data). • Integrated Approach:stores spatial and attribute data using the same data model (typically using the relational data model in a single RDBMS). Hybrid vs. Integrated Approaches

16. Designed by ESRI for ArcView Implementation of the spaghetti vector model An individual layer stores a single type of geometry (i.e. point, line, polygon) No topology (but it can be calculated on the fly...) Draws relatively fast ‘Open’ file format ESRI Shapefile

17. Three primary files in a shapefile: .shp, .shx, and .dbf • All files must share the same prefix for one shapefile, • e.g. road.shp, road.shx, and road.dbf • .shp : stores the feature geometry (binary) • .shx : index for .shp file • .dbf : attribute data stored in dBASE format ESRI Shapefile

19. ESRI Shapefile

20. Designed by ESRI for ArcInfo Implementation of the vector topologic data model ‘Closed’ file format Each coverage is a directory, with numerous files that store feature geometry, projection, registration, etc. Attribute data is stored in a separate INFO directory, which stores all attribute data for all coverages in its parent directory. ESRI Coverage

21. Designed by ESRI for ArcGIS Integrated approach implementing spaghetti vector data model in a relational DBMS (for vector) RDBMS is powered by Microsoft Jet (Access) or other DBMS Topology is generated on the fly Supports versioning, multi-user edits, client-server architecture, other mainstream database functionality ESRI Geodatabase

22. Raster Data Model • A raster representation is composed a series of layers, each with a theme • Typically used to represent ‘field-like’ geographic phenomena

23. Regular Tessellations Squares Triangles Hexagons

24. Irregular Tessellations

25. Raster Grid • but most common raster is composed of squares, called grid cells • grid cells are analogous to pixels in remote sensing images and computer graphics

26. 1 1 1 2 3 1 1 1 2 3 2 2 2 2 2 4 4 4 2 3 4 4 4 2 3 Raster Resolution The distance that one side of a grid cell represents on the ground = grid cell resolution The higher the resolution (smaller the grid cell), the higher the precision, but the greater the cost in data storage

27. Raster Data: Encoding

28. Raster Data: Encoding

29. 1 1 1 2 3 1 1 1 2 3 2 2 2 2 2 4 4 4 2 3 4 4 4 2 3 Raster and RDBMS Raster layer can be attached to a RDBMS ID Land Use • 1 Agricultural • 2 Road • Residential • Industrial

30. Raster Data: ArcGIS

31. Raster Data: ArcGIS

32. Raster in ArcGIS – Floating Point

33. Raster in ArcGIS - Integer