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Raster

Raster can also be referred to as a grid (or cell-based) data structure. Space is divided into regular cells (usually square) so information is stored as a grid or cells/pixels.

Raster DEM

• The location of each object is defined by the row and column position of the cells that they occupy.
  
  
• The area of each cell defines the spatial resolution of the data set.
  
  
• The value for each cell defines the type of object present at that location. Each grid cell has attribute values.
  

The two-dimensional array of cells for a particular theme is called a coverage.

Both vector and raster approaches represent spatial information as homogeneous units. In the case of the vector approach, homogeneous units are points, lines and polygons. In the case of the raster approach, homogeneous units are cells.

Advantages and disadvantages of raster data structures

Advantages

• Simplicity and ease of processing
  
  
• Simple relationships of grid structures to coordinate geometry
  
  
• Overlay functions are easily implemented
  
  
• High spatial variability is efficiently represented
  
  
• Can incorporate remote sensed data and conduct efficient manipulation and enhancement of digital images

Disadvantages

• Coarse quality maps - graphics are less aesthetically pleasing than vector output because instead of producing smooth line boundaries raster output has a blocky appearance.
  
  
• Large data volumes - less compact data storage than vector so data compression techniques are needed to overcome this.
  
  
• Topological relationships are difficult to represent

   

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