Presentation on theme: "GUS: 0262 Fundamentals of GIS Lecture Presentation 4: Vector Data Model Jeremy Mennis Department of Geography and Urban Studies Temple University."— Presentation transcript:
GUS: 0262 Fundamentals of GIS Lecture Presentation 4: Vector Data Model Jeremy Mennis Department of Geography and Urban Studies Temple University
Spatial Data Models 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
Spaghetti Vector Data Model 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. IDCoordinates 13,4 25,5 1 2 For Points:
Spaghetti Vector Data Model 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. IDCoordinates 1(0,1), (3,4), (5,6) 2(3,1), (5,2), (4,3) 1 2 For Lines:
Spaghetti Vector Data Model 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. IDCoordinates 1(2,4), (4,3), (3,6), (2,4), 2(3,1), (5,2), (4,3), (3,2), (3,1) 1 2 For Polygons:
Spaghetti Vector Data Model Advantages simple efficient for display and plotting Disadvantages inefficient for most types of spatial analysis
Vector Topologic Data Model 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
A B C a1a2 a3 a4 n1 n2 ID Arcs A a1, a2 B a2, a4 C a3, a4 Polygon Topology NodeArcs n1a4, a2, a1, a3 n2a2, a4, a3, a1 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 Arc Topology ArcStartXYIntermediateXYEndXY a14,5(4,8), (8,8), (8,1), (4,1)4,3 a24,5(6,7), (6,3)4,3 a34,5(1,3)4,3 a44,34,5 Arc Coordinate Data Vector Topologic Data Model
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 vs. Spaghetti 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)
Hybrid vs. Integrated Approaches 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).
ESRI Shapefile 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 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 Coverage 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 Geodatabase 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