Tuesday, October 13, 2015

Analysis functions in GIS

GIS ANALYSIS FUNCTIONS
GIS analysis functions fall into four categories:
  1. Retrieval/Classification/Measurement functions
  2. Overlay functions
  3. Neighbourhood functions and
  4. Connectivity functions
  • Retrieval functions basically involve a selective search
Classification/Reclassification functions involve two operations:
  1. Identifying a set of features as belonging to a group and
  2. Defining patterns
Measurement functions measure distances, lengths, perimeters and areas

A selective search is an example of a retrieval function. It involves selection of attributes based on graphic selection tools used to select areas in the map displayed.

Overlay functions could be:
  1. Arithmetic 
    1. Addition
    2. Subtraction
    3. Multiplication
    4. Division
  2. Logical
    1. Used to find where specific conditions occur (and, or, >,< etc)
Vector methods are good for sparse data sets while raster methods are easier for grid calculations

Neighbourhood functions
The basic functions that fall under this domain are:
  1. Average
  2. Diversity
  3. Minimum/Maximum and
  4. Total
The parameters that need to be defined to operate these functions are:
  1. Target locations
  2. Specification of neighbourhood
  3. Function to be performed on neighbourhood elements
  4. Search operation is one of the most common neighbourhood function
  5. Neighbourhood function on a vector model is a specialised search function while on a raster model, polygons are on a separate layer and points and lines are on a separate layer.
  6. Theissen polygon operation