Transcript Chapter 3
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