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- Lecture 3:
GIS Data Models
- AIM: To introduce various GIS data models
After this lecture you should be able to:
Describe the primary Vector data models
used in GIS and give examples
Describe raster data models and give
examples
Describe TIN data models
Explain “topology”
Describe the main file formats used in GIS
- Graphic Features
Objects which are shown on a map are
called graphic features or features.
These features may be natural or man
made objects.
- Graphic Features
Digital representation of physical or man made
elements:
Vectors
Points or Nodes
Lines or Arcs
Polygons
Raster Cells or Pixels
Images
Digital Orthophotography
- Geographic Data Types
Images
Vector
Raster (GRID)
Attributes
TIN (Triangulated Irregular Network)
Annotation
© Paul Bolstad, GIS Fundamentals
- Geographic Data Types
© Paul Bolstad, GIS Fundamentals
- DIGITAL SPATIAL DATA
• RASTER
• VECTOR
• Real World
Source: Defense Mapping School
National Imagery and Mapping Agency
- Electronic Maps in Raster and
Vector Formats
- Raster Data Sources
Air Photos
Satellite
Imagery
Scanned Maps
- Digital Orthophotograph
A scanned photograph that
has been mathematically
rectified to eliminate the
effects of displacement so
that its view always appears
as though it is perpendicular
to the ground.
Image
Copyright 1993 Nassau County, NY
- Scanned
Document
- Raster Maps (images)
A set of colored pixels
representing chart
information as a picture on
computer screen
Simply an array of pixels
arranged in rows and
columns
Pixels are color coded, but
do not represent features
explicitly
Rasters can have value
attached
Source: Defense Mapping School
National Imagery and Mapping Agency
- The Appeal of Raster
Looks like a paper map
Cheap and easy to produce (scan
existing paper chart)
Runs easily on PC
World-wide availability w/updates
available
Problems:
Datum may or may not be WGS84
Does not allow automated grounding
avoidance or any other computer-
aided analysis
Storage not as efficient
Source: Defense Mapping School
National Imagery and Mapping Agency
- Vector Data
An intelligent form of digital
geographic data where real world
objects are represented by points,
lines and polygons. An objects
representation is described by
attributes and coordinates.
Examples include:
Digitized Maps
GIS Data
Source: Defense Mapping School
National Imagery and Mapping Agency
- Linking Attributes and
Graphics
In addition to Geography,
GIS is also about
Information. A GIS marries
the capabilities of computer
mapping with database
management systems. So,
a geospatial analyst can
“click” on a geographic
feature and find out
information about it. Or,
they can query the database
to find out information about
all the geographic objects
that meet a specific criteria.
Information about a
geographic object is called
an attribute.
- Linking Attributes with Graphics
In this example, the
user has issued a
query to select all
the properties
whose classification
is single family
residential (210),
and colored the
selection red.
- Vector Data is Layered
•• 2 •
Features:
•
1
5 Line
• Points:
• Connected
•
Lake • 4
Detached
• Area
••
7 6
Text
Spatial Data Analysis
30ł 30’ N 30ł 30’ N
040ł 40’ E 040ł 50’ E
Geographic data are separated
into themes, tiled for speed of
access and placed on CD-ROM Network Analysis
Source: Defense Mapping School
National Imagery and Mapping Agency
- Paradigm Shift
May look “different” from a
paper map (software-
dependent)
Underlying database allows
queries and layer selection
Zooming reveals detail
Complex, expensive, and
time-consuming to produce
Source: Defense Mapping School
National Imagery and Mapping Agency
- Raster and Vector Data Models
Real World
600
1 2 3 4 5 6 7 8 9 10
1 B G Trees
500
2 B G G
3 B
400
4 BG G Trees
Y-AXIS
5 B G G 300
6 B G BK House
7 B 200
8 B B G River
9 B 100
10 B 100 200 300 400 500 600
X-AXIS
Raster Representation Vector Representation
Source: Defense Mapping School
National Imagery and Mapping Agency
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