__GIS ANALYSIS FUNCTIONS__
GIS analysis functions fall into four categories:

- Retrieval/Classification/Measurement functions
- Overlay functions
- Neighbourhood functions and
- Connectivity functions

- Retrieval functions basically involve a selective search

- Identifying a set of features as belonging to a group and
- 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:

**Arithmetic**- Addition
- Subtraction
- Multiplication
- Division
**Logical**- 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:

- Average
- Diversity
- Minimum/Maximum and
- Total

The parameters that need to be defined to operate these functions are:

- Target locations
- Specification of neighbourhood
- Function to be performed on neighbourhood elements
- Search operation is one of the most common neighbourhood function
- 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.
- Theissen polygon operation