On Fri, 20 Dec 2019 at 22:05, Graeme Fitzpatrick <graemefi...@gmail.com> wrote:
> > But would they still count as either =trunk or =primary? > > While they're of high local importance, they're definitely not > high-performance & they don't link major population centres either? > You have just identified three orthogonal dimensions: - Construction (what you call "performance": motorway or dirt track) - Traffic (number of vehicles per hour) - "Importance" (read on) Depending on the country (or area of a country) those three may be highly correlated or loosely correlated. And even within a given area of a given country, the degree of correlation may vary. I put "importance" in quotes because I think it's really routeing. If the only way of getting from A to B is along a particular road, it's very important. If you can get from A to B via many routes, but one is by far the shortest, it's probably important. OTOH if, of the many routes from A to B, one is very much shorter than the others but one of the others takes far less time to traverse then that second one is probably more important. So I think "importance" really means "routeing" (feel free to contradict me). So how do we represent these three dimensions on a map? I'd say we go primarily by construction (with some concession to legalities, because motorways/ freeways/autobahns have legal constraints that differ from other highways). Traffic rates are irrelevant to what is physically there (but have some bearing on choosing a route) and routeing is a decision left to algorithms. Note that routeing algorithms can be run by a computer or they can be run by wetware in a human brain looking at representations on a map. So... Is the route between A and B a motorway or a dirt track? This is important for routeing algorithms on computers and in human wetware because it indicates typical speed limits, legal requirements, etc. Is this the shortest route between A and B? A routeing algorithm can determine that whether it's represented as a motorway or a dirt track, and so can a human looking at a map. Is it the fastest route between A and B? A routeing algorithm can determine that from speed limits, but wetware is aided by seeing if the map renders it as a motorway or a dirt track. Is it important? Depends whether you want to go from A to B or not, but the desirability of using it to get from A to B is down to routeing algorithms (whether computer or human wetware). So I come down firmly on construction (as modified by legislation0. That's verifiable. All else is essentially routeing, whether done by computer or done by wetware in a human brain looking at a map. Want to get from A to B? That's what the query tool in standard carto is for. Maybe one day it will offer the choice of "fastest" and "shortest" (maybe it already does). Or just look at the map, as we boomers are used to from looking at printed maps, and figure out what the best route might be. Do we need to broaden our classes of construction/legality somewhat to encompass standards in countries outside the UK? Probably. Are the values for the highway key UK-centric and somewhat misleading? Sure. Should we map dirt tracks between Hell's Bumhole and Arse-end Of Nowhere as motorways because they're the only way of getting from one place to the other? No, no, a thousand times no. -- Paul
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