> I would expect that a road shown as e.g. trunk in Massachusets would be quite > similar in characteristics to a road shown as trunk in Montana.
Characteristics always change strongly between rural areas and urban areas: in most places a highway=primary will have several lanes in a large city, but in a rural area it will usually be only one lane each way. In a city the speed limit will often been 40 kmh (25 mph), but in a rural area it might be 80 kmh (55 mph) on the same class of road. Similarly, near-wilderness areas like Alaska can be expected to have different road characteristics than more densely-populated rural areas. > try to solve the problem of roads in low-zoom maps at the rendering level, by > modifying the list of displayed road classes until a target density of > displayed roads is reached That's the right solution for maps that are designed for a particular region or country, but it is not feasible for automatically generated maps with global coverage (like the 4 styles shown on openstreetmap.org). The big problem is what happens at the borders between areas: it could be quite confusing if the color or zoom level of a certain highway tag suddenly changed at the border between Spain and France for example. - Joseph Eisenberg On 12/21/19, Wolfgang Zenker <wolfg...@lyxys.ka.sub.org> wrote: > * Joseph Eisenberg <joseph.eisenb...@gmail.com> wrote: >> Above it was said that the highway=trunk vs highway=primary >> distinction is mostly for routing applications. But allowing a proper >> rendering is also a main goal of the road tagging system. > >> While it's true that road class is useful for routing when there are >> two alterate routes, a main reason to tag highways with a certain >> class is to be able to render maps properly at different zoom levels. > >> When you are making a high-scale, low-zoom-level map of a large area >> (say, the whole State of Alaska, all of England, or all of Australia), >> you will want to only render highway=motorway + highway=trunk, because >> showing all highway=primary would lead to rendering many smaller roads >> which are not reasonable to show at that scale in most places. > >> [..] > > What makes the problem of road classification so hard is that we want it > to do different things at once. For rendering we have on the one hand > the requirement that we want to show all the "relevant" roads for a > given zoom level, on the other hand, as a map user I would expect that > a road shown as e.g. trunk in Massachusets would be quite similar in > characteristics to a road shown as trunk in Montana. > > I suggest to keep the road classification consistent at least within > a country and try to solve the problem of roads in low-zoom maps at > the rendering level, by modifying the list of displayed road classes > until a target density of displayed roads is reached. That might > become easier to do when we move to vector tiles. > > Wolfgang > ( lyx@osm ) > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging > _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging