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GUS: 0262Fundamentals 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.
ID Coordinates
1 3,4
2 5,5
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.
ID Coordinates
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.
ID Coordinates
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
Ca1a2
a3 a4
n1
n2
ID Arcs
A a1, a2
B a2, a4
C a3, a4
Polygon Topology
Node Arcs
n1 a4, a2, a1, a3
n2 a2, 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
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
Vector Topologic Data Model
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
