Geographic Information Systems: An Introduction, 3rd Edition

15.1 Network and Raster Connectivity Operations

Connectivity operations, which utilize sets of functions that exploit the connectivity in data, include:

• Network operations
• Contiguity
• Spread functions
• Streaming

Network operations are performed on vector data. Spread functions, streaming, and some connection operations are performed primarily on raster data.

15.1.1 Network operations

Many GISs support analyses in networks, which are systems of connected lines represented in vector data (Figure 15.1). In the real world, networks consist of road systems, power grids, water supply systems, sewerage systems, and the like, all of which transport movable resources. Network operations are based on:

• Continuous, connected networks
• Rules for displacements in a network
• Definitions of units of measure
• Accumulations of attribute values due to displacements
• Rules for manipulating attribute values

GIS network operations usually include:

• Displacement of resources from one place to another (route optimization; Figure 15.2)
• Allocation of resources from/to a center

Figure 15.1

Network analyses can enable a system to find the fastest route between start and end points. Resistance (time delay) is entered as an attribute, and the route with least resistance is selected. (Adapted from ESRI 1995.)

These operations are best described through the example of transport analyses.

As is the case for other ...