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 Advantages

The 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 Advantages

The 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. RASTER

Raster Vector

Want 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