Performing a Shortest Path
Trace

Using a network topology,
which is made up of drawing objects and their relationship data,
you can calculate the shortest path between two points in a drawing
or determine the optimal route based on values of direction and resistance.
This process is known as a *shortest path trace analysis*.

In a drawing of a street network, for example, you might find the shortest path between a fire station and a school.

Shortest path trace based on resistance (time taken to traverse a segment).

You can specify a resistance for any link in the network. This resistance specifies the difficulty in traversing the link. The default resistance is the length of the link.

If a path has a total resistance lower than the Minimum Resistance value, the path is ignored. Similarly, if a path has a total resistance greater than the Maximum Resistance value, the path is ignored.

If you specify an expression that uses SQL data, the Link Template list includes only link templates for the drawing where the topology is loaded:

- In the source drawing, if you loaded the topology from source drawings
- In the current drawing, if you loaded the topology from the current drawing.

Travel Time in Network Topologies

To carry out network path trace analysis on a road network based on time rather than distance, assign a speed or speed limit to each link using an object data field or a field in a linked external database. You then set the Link Direct Resistance property to an expression that uses this speed limit data, for example:

(/ .length (* :speed@street_data 5280))

which divides the length of each link by the average speed per foot (where 5280 is the number of feet in a mile).

The resulting analysis shows the shortest route, in terms of time, not distance, to get from the first point to the second.