Basics of Hierarchy

Discussion created by przemekbielecki on Jan 24, 2011
Latest reply on Jan 26, 2011 by mrice-esristaff
I am a complete beginner and when I say beginner I mean that I am on the tutorial level. So it will be probably very easy to answer my question:)
I read about Hierarchy in Network Analysis when finding the shortest path between two points. From what I understood whenever the "Use Hierarchy" button is checked the solver goes simultaneously from origin and end points omitting lower hierarchy roads whenever it gets to a higher hierarchy road (if it starts at the HierarchyMultinet 5 then omit roads in this category as soon as it finds the HierarchyMultinet 4 then 3 and so on). The on line Arc GIS help says that the solver may not find the solution and fail. When can that happen?? In my case I try to find a shortest way between 1 Cam Alto  and 4995 Hedge Ln (San Francisco"Exercise 3, Network Analyst"), and everything works perfectly fine when I look for the best route with Hierarchy on. However when I add some polygon barrier span between 92 Marina Green Dr, 63 Green St, 84 Zoe St, 331 Lake St the solution fails. I followed the HierarchyMultinet of each element of the found connection in both cases and they are built similarly. I mean in the first case the solution follows the 5th hierarchy then converts to 4th then 3rd then 2nd then goes to the 3rd again then again to the 2nd...why if the Hierarchy is checked on!!?? The same is in the second case but this time the Hierarchy is unchecked...I can understand that:) but I still don't get the meaning of the hierarchy in the first described  case. Can somebody try to shed some light on this??

Thank you