Friday, October 23, 2015

Connectivity functions

CONNECTIVITY FUNCTIONS
Connectivity functions examine relationships between objects in terms of adjacency and relative-effective-distance. Operators associated with connectivity include:
-Network analysis
-Diffusion models
-Cellular automata and
-Agent based models

The two connectivity functions widely used in GIS are:
-Contiguity and
-Spreading

Contiguity analysis exploits the topological relationships between objects. It helps determine if two objects are adjacent or if they share a node. Contiguity analysis also helps determine a pattern of spread.
Grouping vector data is used to reclassify a map and dissolve polygon boundaries. Grouping is also done on raster data but is less elegant than grouping operation on vector data.

Contiguity is used to measure shortest and longest straight line distances across and area and to identify areas of terrain with specified size and shape characteristics.

Proximity Functions. The simple distance between features. Four parameters are used to measure proximity are listed below
1. target locations.
2. unit of measurement.
3. a function to calculate proximity and
4. the area to be analyzed.

A common type of proximity analysis is the buffer zone.

Network Functions
A network is a set of interconnected linear features that form a pattern or framework. City Streets, Power Transmission Lines, and Airline Service Routes are examples.
There are three principal types of GIS Analysis performed by Networking.
1. Prediction of loading on the network itself (prediction of flood crests),
2. Rate optimentation (emergency routing of ambulances), and
3. Resource allocation (zones for servicing rescue areas)

Networks analysis entails four components.
1. set of resources (goods to be delivered)
2. one or more locations where the resources are located (several warehouses where the goods are located)
3. an objective to deliver the resources to a set of destinations (customer locational data base) and
4. Set of constraints that places limits on how the objective can be met (is it economically feasible to deliver goods from one point to another)

Spread Functions
Spread functions help determine the "BEST" way to go from point A to point B

Seek or Stream Functions
Seek or Stream Functions refer to a function that is directed outward in a step-by-step manner using a specified decision rule. This function can be used to evaluate erosion potential.

Intervisibility functions
This function is a graphic depiction of the area that can be seen from the specified target areas. Intervisibility functions rely on digital elevation data to define the surrounding topography.