I creataed a simple service layer polygon in network analyst(ArcGIS Desktop 10.2) with no heirachies set in the street network. Now I don't udnerstand why is this polygon created along some particular streets? Why isn't is properly spread out? For example why doesnt the polygon cover the areas/streets I have marked in red?(obviously those marked areas are also within 1km atleast, then why not form there?) The impedence is 1km and 2kms respectively. The streets are also well connected individual line elements as you can see the junctions.
Not sure if you found an answer already, but I'll throw out some ideas in case you haven't:
1. The most common reason for this to occur is that the street linework is not truly connected from a Network Analyst perspective. It can look fine visually, but will have tiny disconnects that prevent the passage from one edge to another. Run Topology with rules to check the linework and then edit the data to resolve this.
2. Another reason could be that the attributes that Network Analyst checks to determine if a route can be used are set incorrectly. For example, the "oneway" attribute may be set up incorrectly.
Chris Donohue, GISP