Poles, Wires, Corners, and Street Openings
A long urban route may use many separate doorways. Each one must be valid, and the end of one section must connect to the beginning of the next.
Every wire must stand over its posts
A city route often borrows utility infrastructure that was built for electricity or communications, not for an eruv. The overhead line must nevertheless relate correctly to the posts halacha recognizes as the sides of its doorway.
A utility wire can be moved to another attachment point, a lechi can be displaced, and a pole can be replaced without preserving the old alignment. The line may still look continuous from a car while the halachic doorway has disappeared.
Corners and changes in direction
When the route turns, the two boundary lines must meet. Parallel wires that stop near the same intersection do not necessarily close the diagonal space between them.
The accepted route should identify the exact pole, lechi, wire, and connection at every corner. Otherwise an inspector cannot know which physical form must be preserved after utility work or construction.
Open streets through the route
A street passing through the claimed enclosure may create a breach. Its width, direction, public use, and status as a possible reshus harabim affect whether an ordinary tzuras hapesach is sufficient.
This question cannot be answered by looking only at the wire overhead. The road must be considered as part of the city network, including where it enters and where it continues beyond the proposed boundary.
A chain with no missing doorway
A route made from hundreds of doorways is valid only when they form one continuous enclosure. One untreated opening can leave the area open even if every other section is carefully constructed.
Maps are useful for following that chain, but the psak depends on the actual structures on the street and the halachic status assigned to each one.