Chapter 3

Report
METHODS
OF REPRESENTING
GEOGRAPHIC SPACE
Raster Model
Vector Model
MAP AS AN ABSTRACTION
OF SPACE:
Spatial features can be represented as points,
lines and area(polygons).
 Some objects are selected for inclusion and
another not spatial feature and it have
attributes as 1- simplified 2-aggregated 3classified.
 When the geographies want to enter the data to
GIS, they have some decision need to made
based upon to can entered it to computer.

THE DEFINITION:
Raster Models:
It is that features made of cells and each cells
related with another cells.

Vector Models:
It is that features included points, lines and
polygons and their data is spaghetti.

VECTOR MODELS

It is represent by (x , y) coordinates.

Vector model take less storage.

Example for vector model is digitization.

We take long time when make vector model.
RASTER
MODELS

It is represent by (pixel or cell)

It is take more storage.


Example for raster model is scanning.
We take short time when make Raster model.
GEOGRAPHIC REPRESENTATIONS


CELLS: a representation of geographic data
on rows and columns .
PIXELS: a group of points with a color value
but no data related to others
RASTER
AND VECTOR REPRESENTATION
Raster
representation
Vector
representation
CONTINUE
RASTER DATA: ADVANTAGES
AND
DISADVANTAGES
Advantages
Disadvantages
Due to the nature of the data
storage technique data
analysis is usually easy to
program
The cell size determines the
resolution at which the data
is represented
The inherent nature of raster
maps
Processing of associated
attribute data may be
cumbersome
Discrete data
Raster maps normally reflect
only one attribute for an area
Grid-cell systems are very
compatible with raster-based
output devices
most input data is in vector
form, data must undergo
vector-to-raster conversion
compatible with digital
satellite imagery
Most output maps from gridcell systems
VECTOR DATA: ADVANTAGES AND DISADVANTAGES
Advantages
Disadvantages
Data can be represented at its
original resolution without
generalization.
The location of each vertex
needs to be stored
Graphic output is usually more
accurate
For effective analysis, vector
data must be converted into a
topological structure
Accurate geographic location of
data is maintained.
Topology is static
Because it recognizes entities,
model allows for efficient
encoding of topology
Algorithms for manipulative
and analysis functions are
complex
Continuous data, such as
elevation data, is not
effectively represented in
vector form.
GRID
DATA (CELLS)
SATELLITE
IMAGE (PIXELS)
VECTOR VS. RASTER
Vector
Raster
Storage space
Want little space
Want more space
Topology
easy
difficult
Aesthetic
Arces more
aesthetically
pleasing
Grides not very
aesthetic
Data structures
More complex
More simple
Geographic
specificity
better
limited

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