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

Spatial Data Models

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. For Points: ID Coordinates 3,4 5,5 2 1

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. For Lines: ID Coordinates (0,1), (3,4), (5,6) (3,1), (5,2), (4,3) 1 2

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. For Polygons: ID Coordinates (2,4), (4,3), (3,6) , (2,4), (3,1), (5,2), (4,3), (3,2), (3,1) 1 2

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

Vector Topologic Data Model B C a1 a2 a3 a4 n1 n2 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 Arc Coordinate Data 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 Node Arcs n1 a4, a2, a1, a3 n2 a2, a4, a3, a1 Node Topology ID Arcs A a1, a2 B a2, a4 C a3, a4 Polygon Topology

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)

Triangulated Irregular Network (TIN)

Triangulated Irregular Network (TIN)

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 Shapefile

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