On Sat, 10 Aug 2019 at 09:27, Joseph Eisenberg <joseph.eisenb...@gmail.com> wrote:
However, in England where the tag originated, highway=trunk is used for the > main, > non-motorway highways in the country. > Erm, no. It's not like that. Almost, but not quite. There are A roads (known in OSM as primary routes) which are important routes connecting major population centres. There are B roads (known in OSM as secondary routes) which have lower traffic densities than A routes and/or connect lesser population centres. "A" roads are not synonymous with trunks in the UK. In the UK a trunk road is more of an A+ road rather than just an A road and is funded/maintained by national government rather than local government. Ignoring motorways, all(?) UK trunks are A roads but not all A roads are trunks. As far as motorists are concerned, trunks are indistinguishable from A roads in terms of signage. Although a non-trunk A road usually does not have the capacity of a trunk A road there are cases where that is not true. And then there are motorways. In OSM-speak they might be called nullary (nihilary?) routes. "A" roads are level 1, B roads are level 2 and motorways are level 0. Trunks are maybe level 0.9 or 0.75 or 0.99 or something like that - a little better than non-trunk A roads, maybe. See https://en.wikipedia.org/wiki/Roads_in_the_United_Kingdom#Classification As can be seen by glancing at the rendering of > England, these highway=trunk connect just about every place=town in > England: https://www.openstreetmap.org/#map=6/53.021/-1.033 Assuming they have all been tagged correctly, of course. That may not be the case. The idea is that one can determine the classification of highway based > on what size of settlements it connects: > > trunk - connects cities to cities ("National Roads") > primary - connects a town to a city or another town > secondary - connects a village to a town/city or another village > tertiary - connects a hamlet to a village/town or another hamlet > unclassified - connect farms / isolated dwellings to a hamlet/vilage > or another farm. > In general, I dislike it when different countries interpret the same tags differently. But I also don't like the possibility that OSM will render routes in a way that differs from their official classifications. Civil servants have examined actual traffic statistics and considered actual road construction (bends, constrictions, junctions, etc.) to classify certain routes in certain ways. If they say that the shortest road between town X and town Y is a B road rather than an A road, they had a good reason to do so (I hope). Your scheme also suffers another problem. I can point you at a road which connects the biggest town in my county to the biggest (only) city in my county. It passes through a smaller town and a large number of hamlets. Is it a primary (big town to city) or a secondary (hamlet to hamlet to hamlet)? You may think it's obvious, but there are any number of circuitous routes connecting that big town to the city. I can come up with a route that takes me the thirty miles from the big town to the city by wandering to the other end of the UK and back, but hat route DOES connect the two. Equally, the shortest route between X and Y could be a twisty, bendy thing whilst there's an A road and a B road that connect the two which are longer but faster. This system is internally consistent and works well for rendering, as > well as for routing. > Shortest route vs fastest route. UK road designations take both factors into account, mainly the latter. People eyeballing things are likely to come up with the former. -- Paul
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