methods of representing geographic space
Post on 24-Feb-2016
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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 3- classified.
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
Vector representation
Raster representation
CONTINUE
RASTER DATA: ADVANTAGES AND DISADVANTAGES Disadvantages AdvantagesThe cell size determines the resolution at which the data is represented
Due to the nature of the data storage technique data analysis is usually easy to program
Processing of associated attribute data may be cumbersome
The inherent nature of raster maps
Raster maps normally reflect only one attribute for an area
Discrete data
most input data is in vector form, data must undergo vector-to-raster conversion
Grid-cell systems are very compatible with raster-based output devices
Most output maps from grid-cell systems
compatible with digital satellite imagery
VECTOR DATA: ADVANTAGES AND DISADVANTAGES
Disadvantages AdvantagesThe location of each vertex needs to be stored
Data can be represented at its original resolution without generalization.
For effective analysis, vector data must be converted into a topological structure
Graphic output is usually more accurate
Topology is static Accurate geographic location of data is maintained.
Algorithms for manipulative and analysis functions are complex
Because it recognizes entities, model allows for efficient encoding of topology
Continuous data, such as elevation data, is not effectively represented in vector form.
GRID DATA (CELLS)
SATELLITE IMAGE (PIXELS)
VECTOR VS. RASTERRaster VectorWant more space Want little space Storage space
difficult easy Topology
Grides not very aesthetic
Arces more aesthetically pleasing
Aesthetic
More simple More complex Data structures
limited better Geographic specificity
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