Geometric Networks Francisco Olivera, Ph.D., P.E. Srikanth Koka Department of Civil Engineering Texas A&M University

Networks Dentritic networks Loop networks

Geometric Networks A geometric network stores line/junction connectivity. E.g., A water network consisting of water mains, valves, pump stations etc. To build and edit geometric networks, ArcInfo 8.x or ArcEditor 8.x is needed. ArcCatalog or ArcToolBox can be used to build geometric networks.

Geometric Networks ArcMap is used to edit or analyze geometric networks. Network analysis can be done using the Utility Network Analyst. To build a new geometric network, right click a feature dataset, then click on New/Geometric Network.

Edges and Junctions A geometric network consists of edge network features and junction network features. Edges are network features similar to simple line features. E.g., water mains. Junctions are network features similar to simple point features. E.g., valves. Edge – Edge connectivity is built through junctions. Junction Edge

Simple and Complex features Simple edge features: Edges end with junctions and junctions connect edges. Complex edge features are created by connecting features to an edge without splitting them at junctions.

Snapping Snapping is a process moving features. For example making line ends and junctions coincide. Snap tolerance defines the maximum distance a network feature could be moved.

Sources and Sinks Sources and Sinks are used to define the flow direction in the network. Sources are junctions that push the flow away from themselves. Sinks are junctions that pull flow towards themselves. An attribute called ‘Ancillary Role’ defines whether a junction is source or sink.

Flow Direction There are three types of flow directions: Determinate, Indeterminate, Uninitialized. Determinate flow occurs in as edge if a unique flow direction can be assigned. E.g. A dendritic stream network. Indeterminate flow direction occurs in an edge if the flow direction is not unique. E.g. A transportation network. Uninitialized flow direction occurs when the flow in a edge is not influenced by sources and sinks. E.g. A stream network with sources and sinks not defined

Trace Tools Downstream Trace Upstream Trace Trace tasks: Find Common Ancestors Find Connected Find Loops Find Disconnected Find Path Upstream Find Path Trace Downstream Find Upstream Accumulation Trace Upstream

Network weights A weight can be defined as the cost for traversing an element in the network. E.g., pressure loss (per unit length) due to friction in the pipe. Many to zero or many to one relationships exist between attributes and network weights.

Enabled and Disabled features Features in a network can be enabled or disabled. Disabled features act as barriers to flow, whereas enabled features allow the flow to path through. E.g., due to maintenance of a pipe in the network, it may be disabled temporarily. An attribute called ‘Enabled’, set either to 1 or 0, defines enabled or disabled property of each network feature.

Network Connectivity Rules Rules are set in order to define the connectivity between different network features or/and between different feature types (i.e. sub types). Types of connectivity rules: Edge – Junction rules and Edge – Edge rules. Rules can be established such that 10 inch transmission mains connects only to 8 inch transmission mains. To define connectivity rules right click on the geometric network, click Properties, then click on Connectivity tab.

Network Errors Illegal geometries might be encountered when building geometric networks. Common ones: empty geometry, multiple parts, same from and to nodes, zero feature length. The geometric building wizard automatically determines such features and report such features attributes by creating a new table inside the geodatabase.

Repairing Network Topology Network repairing can be done using Network Editing tools. Common tasks that can be performed: Rebuilding connectivity Repairing connectivity Repairing features with an empty geometry or zero length Repairing features with an identical start-stop vertex Rebuilding features with multipart geometry