GIS Data Type
Basic Elements:
•
Location (x,y) or (x,y,z)
•
Explicit, i.e. pegged to a coordinate
system
•
Different coordinate system (and
precision) require different values
1. e.g.
UTM as integer (but large)
2. Lat,
long as two floating point numbers +/-
•
Points are used to build more complex
features
Basic Elements:
•
Extent
1. Rows
2. Columns
•
Origin
•
Orientation
•
Resolution: pixel = grain = grid
cell
Advantages of Vector Data Structures:
•
Good representation of
phenomenonology
•
Compact
•
Topology can be completely
described
•
Accurate graphics
•
Retrieval, updating and generalization
of graphics and attributes possible
Advantages of Raster Data Structures:
•
Simple data structures
•
Overlay and combination of maps and
remote sensed images easy
•
Some spatial analysis methods simple to
perform
•
Simulation easy, because cells have the
same size and shape
•
Technology is cheap
Disadvantages of Vector Data
Structures:
•
Complex Data Structures
•
Combination of several vector polygon
maps through overlay creates difficulties
•
Simulation is difficult because each
unit has a different topological form
•
Display and plotting can be expensive,
particularly for high quality color
•
The technology is expensive,
particularly for the more sophisticated software and hardware
•
Spatial analysis and filtering within
polygons are impossible
Disadvantages of Raster Data
Structures:
•
The use of large cells to reduce data
volumes means that phenomenon logically recognizable structures can be lost and
there can be a serious loss of information
•
Crude raster maps are considerably less
beautiful than line maps
•
Network linkages are difficult to
establish
•
Projection transformations are time
consuming unless special algorithms or hardware is used.
EXAMPLES
•
Administrative borders
•
Linear features
•
Roads
•
Rivers
•
Discrete habitat boundaries
EXAMPLES
•
Temperature (air, water)
•
Air pressure
•
Ecotones
•
Soil ph.
•
Precipitation
•
Salinity
•
Elevation & its derivatives
•
Flow
•
Direction, distance
•
Reflectance (photography/imagery)
VECTOR FORMATS
1. Shapefile
Contains:
· Point,
or multi-point
· Line,
or polyline
· Polygon
2. Coverage
Contains:
· Point,
or node
· Arc,
or line
· Polygon
· Label