So how should a street Elevation be mapped?
- If a seagull can fly right under it, it’s a bridge (level greather than 0).
- If it is underground, it’s a tunnel (level lower than 0)
- For every other case the road is ground level (level = Ground), even if it’s artificially elevated or dug under street level.
We mark bridges with level = +1. In many cases we will need to split segments into two or more segments to correctly mark only the right parts of the road as a bridge or a tunnel.
We only mark a road as level = +2 if there’s another bridge (+1) running underneath it.
Regarding tunnels: It is important that a tunnel segment has GPS lock before and after the tunnel. As we all know, this is impossible once you're in the tunnel so keep the "tight marking" at least 50ft BEFORE and AFTER the tunnel and don't forget to tick the Tunnel checkbox for the segment going through the tunnel.