GUS: 0265 Applications in GIS

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GUS 0265Applications in GIS

• Lecture Presentation 1
• Vector Data Model and Operations
• Jeremy Mennis
• Department of Geography and Urban Studies
• Temple University

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Vector Data Models
Geometric Primitives Points, lines,
polygons Two Primary Types Spaghetti Topologic
(and TIN)
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Spaghetti Vector Data Model
Each point, line, or polygon is stored as a
record in a file that consists of that entitys
ID and a list of coordinates that define geometry.
For Points

• ID Coordinates
• 3,4
• 5,5

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1
4
Spaghetti Vector Data Model
Each point, line, or polygon is stored as a
record in a file that consists of that entitys
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)

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2
5
Spaghetti Vector Data Model
Each point, line, or polygon is stored as a
record in a file that consists of that entitys
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)

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2
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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
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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
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Spaghetti Vector Data Model
Advantages simple efficient for display and
plotting Disadvantages inefficient for most
types of spatial analysis
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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
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Vector Topologic Data Model
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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.
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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)
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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.
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Triangulated Irregular Network (TIN)
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Triangulated Irregular Network (TIN)
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Vector Operations
Classification Buffer Overlay
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Classification
Line Dissolve (Map Dissolve)
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3
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2
1
4
1 grain crops 2 orchards 3 residential 4
commercial
1 agricultural 2 non-agricultural
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Buffer
Definition of what is within/without a given
proximity
Line buffer
Point buffer
Polygon buffer
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Overlay
An overlay operation takes two or more data
layers as input and results in an output data
layer Three types of overlay Point in
polygon Line in polygon Polygon (polygon on
polygon)
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Point in Polygon Overlay
Land Cover
Trees
NewTrees
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2
A
A
C

C

B
B
Point Table
Poly Table
Point Table
ID Cover 1 Rural 2 Urban
ID Tree A Elm B Maple C Elm
ID Tree Cover A Elm Rural B
Maple Rural C Elm Urban
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Line in Polygon Overlay
Land Cover
Streets
NewStreets
C
C
A
A


D
B
B
1
2
Line Table
Poly Table
Line Table
ID Cover 1 Rural 2 Urban
ID Street A Race B Race C
Arch
ID Street Cover A Race Rural
B Race Urban C Arch
Urban D Race Urban
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Polygon Overlay
Intersection (and)
Union (or)
Identity
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Polygon Overlay Intersection
Agriculture
Land Cover
ltIntermediategt
A
A
B
B
ID Owner A Brown B Smith
ID Cover A commercial B industrial
Area of intersection
New node
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Polygon Overlay Union
Agriculture
ltIntermediategt
Land Cover
A
A
B
B
ID Owner A Brown B Smith
ID Cover A commercial B industrial
Area of union
New node
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Polygon Overlay Identity
Agriculture (input layer)
Land Cover (identity layer)
ltIntermediategt
A
A
B
B
ID Owner A Brown B Smith
ID Cover A commercial B industrial
Area of identity
New node