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