Elevations should be mapped more-or-less realistically, with elevation numbers showing where the higher-elevation segments above lower-elevation segments.
If a seagull can fly right under it, it’s a bridge (level greather than 0).
A road is only level = +2 if there’s another bridge (+1) running underneath it.
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.
Tight Marking Roads that have poor or no GPS reception should have the tunnel checkbox set. The road segment must begin at least 50 feet before GPS signal is lost, and continue at least 50 feet after GPS signal is recovered.
Tight Marking. We mark bridges with level = +1. In some cases we will need to split segments into two or more segments to mark only the right parts of the road as a bridge or a tunnel. This is Tight Marking.
At interchanges, where there is already a nearby junction, it will not be necessary to use "tight" marking for an elevation change on the overpass. Use the existing junctions if at all reasonable.
