Network Analysis

Overview

• GIS deals with the interrelated nature of geographic data

• Some data has specialized rules, parameters and restrictions on interaction

• Measurements, relationship-testing and analysis must all occur within this framework

Overview

• Network analysis focuses on edge-node topology to represent real-life networks of information– Driving directions– Multi-modal routing– Information networks– Electricity, water, sewer, natural gas…

Edges and Nodes

• Series of nodes connected by edges– Each edge starts or ends at a node– Each node touches at least one edge– Nodes have one or more edge connecting them

• Planar or non-planar networks– Bridges, tunnels, etc…– Need for topology enforcement

• GIS needs to know what data is part of the network and what is simply just data

OpenStreetMap Routing

• OSM follows the same rules of edge-node networks.

• TIGER data from the Census does not differentiate between over/underpasses

• A procedure for fixing the network connectivity:– Remove the shared nodes– Without shared nodes, ways cross but don’t intersect.

• Real world example of this network topology structure.

Network Properties

• In order for our network to function, we need the following:– Base data (our edges and nodes)– Cost to traverse the network (dist, time, other)– Restrictions on travel (one way, no left turns)– Temporal information – at a given time:• Is there a higher cost to traveling the network? • Are there additional restrictions on our use?

Network Participation

• In ArcGIS, feature classes that participate in a network must all reside within a feature dataset – Feature datasets are only in geodatabases

• The GDB stores additional information about the network and its parts

• Types of network edges, connectivity rules, impedance, etc…

Base Network

• The base network type within ArcGIS is the Geometric Network, enforcing edge-node topology

• Two other network types are available, the routing network and the utility network.– Routing and analysis of multimodal transportation– Analysis and management of utilities

Routing Network Attributes

• Cost (friction, impedance)– Length of edges– Time to travel along edges– Financial cost to traverse network

• Restrictions (barriers, temporary or permanent)– One-way Streets, No Left Turn, etc…– Height/weight (vehicle class) restrictions– Temporal Restrictions (school zones, flooding)

Network Uses

• Once our network is complete, we can perform analysis on our network– Shortest Cost Path– Network Flow– Service Areas– Routing– Connectivity analysis– Health of the network

Network Interface in ArcGIS

• Network Analyst is an extension to the ArcGIS Core

• Extensions must be enabled to use

• Enabled in both ArcMap and ArcCatalog

Network Analysis Toolbar

Menu Working Dataset

Analysis Panel

Create Network Feature

Select Network Feature Solve

Directions

Network Identify

Build

Network Analysis Panel

• Creating a new Route, Service Area, etc. from the Network Analysis menu will add it to the Table of Contents

• The Network Analysis panel provides you additional access to network-derived data