> 1. There is a first classification system using the kind of way going > over it for distinction: >
which is inherent in the way or other structure that is tagged with "bridge": highway, railway, waterway, pipeline > > 1.1 A road (or railway): "viaduct" (a term that is not really well > defined, especially the distinction between a "bridge" and a "viaduct" > doesn't seem to be clear). This is a bit mixed because besides the > road this seems to be a bridge with several abutments in "small" > distances, whatever "small" is, and "viaduct" seems to be used also in > conjunction with railroads. Not sure but I feel as "viaduct" might > also be a bridge typology (see 3). > For me the viaduct is a specific type of bridge, i.e. one that has intermediate pillars in addition to the end supports > > 1.2 Water: "aqueduct" (suitable for the parts of aqueducts that span > over a void). The definition seems to extend the use to all kind of > aqueducts ("A longer structure for carrying a canal or fresh water.") > while many aqueducts are not spanning over something (they are tubes, > have a solid support like a wall without openings or even are > underground) so they clearly aren't bridges. > If it is open water like a canal bridge, this is waterway=canal and bridge=viaduct (for example). If the water flows in a closed structure: man_,made=pipeline type=water bridge=yes This first system doesn't make much sense IMHO, because you can > already see by other tags which kind of way is on top (waterway, > highway, railway), but it is currently the most used. > > > 2. Another classification system on the page is one according to the > structural system employed: > 2.1 arch > 2.2 pontoon > 2.3 suspension > > 3. And even another system is that of typology: > 3.1 bascule > 3.2 drawbridge > 3.3 humpback > 3.4 lift > 3.5 swing > I don't see anything wrong with todays tagging. Bridge is an additional key to the main way (highway, waterway, railway, other man_made structure) that initally can laso be ommitted. The key bridge can have a value that decribes the type of bridge, i.e. yes (generic) viaduct arch pontoon suspension bascule drawbridge humpback lift swing Note that the non-generic bridge types are all mutually exclusive, I do not see the difference between typology and structural system. "so why is this bad?" one might argue. Well, the problem is that with > this chaos you won't be able to tag all properties (typology, > structural system, carried way) of a bridge, you will instead have to > decide which one to focus on (might also lead to tagging wars). > Another problem is that the lack of systematics makes it difficult to > extent this system with new values, because it is not clear where the > focus is. > > > I propose to use distinct tags for these properties instead: > > 1. is not needed IMHO (see above). If the interesting fact for > viaducts are the several "small" spans I'd put this into typology. > 2. could be tagged with bridge:structure (or structure or > structural_system) > 3. could be tagged with bridge:type (or type). > I do not see the need to change the tagging system Last but not least I'd like to ask you for comments on 3 new values: > N1. a bridge made of few ropes where you walk on a rope: > > http://bauwiki.tugraz.at/pub/Baulexikon/HaengeSeilBrueckeB/Kaiserschild_1.jpg > > http://www.gruppenstunden-freizeit-programme.de/ferienlager-freizeiten-erlebnisse/freizeit-bilder/seilbruecke/Piratenlager-05-262.JPG > http://www.bergsteigen.at/pic/d6025434-21f9-4d93-9ce9-42aba5cf00db.jpg > > additionally we could tag the amount of ropes (or even more precisely > the amount of "upper" and "lower" ropes) > > are these described in English with the term "zip-line"? > http://en.wikipedia.org/wiki/Zip-line > > > N2. a similar bridge made of ropes, but you walk on planks: > > http://bauwiki.tugraz.at/pub/Baulexikon/HaengeSeilBrueckeB/Trift_Bruecke_1.jpg > http://bauwiki.tugraz.at/pub/Baulexikon/HaengeSeilBrueckeB/Tripsdrill.jpg > > I guess this would be a "simple_suspension_bridge" > > > N3. A "Cable-stayed_bridge" (the absence of this value makes it > probable that most of these might currently be tagged as suspension > bridges or not classified at all). The difference from a suspension > bridge is that the cables are directly attached to the towers / pylons > instead of to another cable, see here: > http://en.wikipedia.org/wiki/Cable_stayed_bridge > I have got the impression that we are overdoing things here. For me these are all some variants of foot suspension bridges. See http://en.wikipedia.org/wiki/Suspension_bridge and http://en.wikipedia.org/wiki/Simple_suspension_bridge. Volker
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