OpenStreetMap
So, two of my interests are tagging waterways and highways. And of course, where they intersect, there is often a bridge. Here is how my bridge tagging method has progressed over time:
- Bare minimum - split the highway (using e.g. aerial imagery), set
bridge=yesandlayer=1. This is conventional, if not particularly informative.
Then I found the National Bridge Inventory, which contains not all, but certainly many of the significant bridges in the USA. This data is quite interesting, it includes detailed info on the bridge structure and its integrity.
One can use this to verify the length of the bridge as drawn on the map, in many cases what’s shown in aerial imagery matches to within 1-2m of the specified length. You can also find data on when the bridge was constructed or rebuilt.
- Added context - add
start_datetag.
Today, I was thinking, it’s not much more difficult to add an area object for the bridge structure itself using the man_made=bridge tag. In fact, one could then move such tags as start_date and bridge:structure into the separate object.
There is also an existing bridge:ref tag which is loosely defined. Here’s my idea. What if we used the NBI BridgeID, where available (in the USA)? You might wonder why that would be useful. Well there is a site https://bridgereports.com, which parses the NBI database with some additional refinements, and displays a nicely formatted summary. A plugin might use the BridgeID to display such data.
Something like the following. For the highway:
bridge=yes
highway=secondary
layer=1
ref=KY 218
And for the bridge structure:
ref:nbi=044B00032N
structure=beam
layer=1
man_made=bridge
start_date=1978
Here’s how the metadata could be displayed (using bridge ID “044B00032N”): https://bridgereports.com/1211803
Discussion
Comment from lyx on 30 October 2022 at 09:59
I like it. The one thing I think you should change is the ref. Assuming NBI stands for “National Bridge Inventory” I guess more countries in the English speaking world would come up with just the same name, so it might be better to use ref:us:nbi. It would make the task easier for map makers that want to show the link. Otherwise they would have to find out the country first, which is possible of course but might require more computational effort. After looking at the nbi website, the license information for this data appears to be not entirely clear. Maybe it would be better to just add the ref, but not copy the structure and start_date data, just to be safe. Greetings, Wolfgang (lyx@osm)
Comment from Tordanik on 30 October 2022 at 18:03
Nice detail, and having a separate element for the bridge itself definitely makes it much cleaner to add tags to it!
I think
bridge:structureis still used in combination withman_made=bridge, though. Unlikenameorref(where thebridge:prefix is purely for disambiguation with the street’s name), I don’t think it’s supposed to be shortened when used on a bridge polygon.Comment from historic_bruno on 30 October 2022 at 18:25
Thank you for the comments :)
@lyx I agree, after I posted this, I did more research on
ref, and it seems more conventional and less confusing to indicate the country.As for licensing, as a published work of the US government, I believe this data passes into the public domain. I’ll be happy to contact them and ask for clarification!
@Tordanik Indeed, I examined the taginfo for
bridge:structureand it seems used exclusively,structureby itself indicates something different.Comment from lyx on 30 October 2022 at 21:24
@historic_bruno On https://catalog.data.gov/dataset/national-bridge-inventory-national-geospatial-data-asset-ngda-bridges they say that they got no license information from their source, but IF this data was prepared by government employees in the course of their work it would be considered an US Government work. The problem here seems to be that they don’t know if this was the case.
Comment from mboeringa on 18 November 2022 at 19:09
If you do start to add man_made=bridge polygons, please make sure the corresponding highway=x + bridge=x match perfectly by connecting the end nodes of the highway=x + bridge=x way to the man_made=bridge polygon.
Never let it over- or undershoot the man_made=bridge polygon.
This will prevent drawing errors in renderers that take into account the layer=x tag of both features (current ‘openstreetmap-carto’ doesn’t for man_made=bridge, but there are implementations that do).