David Lynch <djly...@gmail.com> writes: >> Motorway: More than one grade-separated intersection in a row, high >> speed, oncoming traffic separated.
A Motorway should meet the physical standards of what the best national Motorway/Interstate/etc. roads are. Generally entirely divided and limited access with on/offramps. If you mean that by 'grade-separated intersections', that's fine. > Trunk: Wide, high-speed roads with limited cross traffic. Usually dual > carriageways in urban areas. I see Trunk as almost motorway, but a little deficient. Definitely has to be divided by at least some concrete (== dual carriageway), and mostly limited access with infrequent at-grade intersections. Urban areas are so crowded that roads that meet this definition have to be basically motorway like but probably more curvy with lanes that aren't wide enough, and have too many on/offramps. Example for those who know Boston: http://www.openstreetmap.org/?lat=42.35331&lon=-71.10166&zoom=15&layers=B000FTF Storrow Drive is trunk (limited access), while Memorial Drive is primary (side streets come out to it). Both have underpasses for through traffic, but Memorial Drive sometimes and Storrow Drive ~always. And west of boston; http://www.openstreetmap.org/?lat=42.4355&lon=-71.2795&zoom=14&layers=B000FTF Here SR2 is divided ("Jersey barriers", just 0.5m wide x 1m high concrete), and there is maybe 1 farmstand per km, and perhaps 5km between intersections. To the East it's motoray (you really could not tell it's not an Interstate except for the signs, or maybe there are a few too many exits). (I need to retag 2 inside 128 as motorway.) So for motorway and trunk we are still talking physical, although physical and important correlate very very well. > Primary: In rural areas, a major road between cities which does not > meet motorway or trunk standards. In urban areas, a major road which > is particularly long or heavily traveled, or the extension of a road > which is primary outside the urban area. Here the notion of 'cities' is problematic. In Mass, city is a legal term, and some are only 30000 people. If you mean 'by city, someplace that's big enough to have a self-identity as an urban center, as opposed to viewing itself as part of some larger urban center", that's fine. > Secondary: Other major urban streets not meeting the standards for > primary. Also highways in rural areas. I have the notion that secondary should be at least a state highway or a road that goes considerable distance and is used for medium-distance travel, meaning a significant number of people drive 20km or more on it. > Tertiary: City streets that have a median, more than two lanes, and/or > moderate traffic, but are low speed and primarily residential, or > locally-maintained rural roads that are important for local > navigation, such as connecting a shortcut between two nearby highways > which don't intersect. "locally-maintained"??? Who paves a road is highly variable by jurisdiction and not relevant to this classification. My real problem with the split urban/rural approach is that we're sort of defining by distance, and sort of by population. Importance (to whom) is some blend of these. I live outside the city, so I see the (existing) "primary goes many many towns", "secondary goes multiple towns" and "tertiary goes to the next town, or is a major road for getting around town" definition as very natural. In the city, there are vastly more roads, and if this rule were applied there would be a large number of tertiary and then a huge number of residential/unclassified roads. From my country point of view this is correct. But when I look at Cambridge (a city I lived in for 12 years, 6 of them with a car), I see vast numbers of 'secondary' roads that are not in my view even close to secondary status: http://www.openstreetmap.org/?lat=42.3658&lon=-71.0996&zoom=14&layers=B000FTF and a lot of tertiary roads that seem overrated. The root of the problem is that if you look at Camrbidge and Stow at the same zoom level: http://www.openstreetmap.org/?lat=42.4357&lon=-71.504&zoom=14&layers=B000FTF a road of a length marked tertiary in Cambridge goes by 15 little streets is just a road with 20 houses on it and maybe a cross street. So, from the distance point of view, roads in Cambridge are grossly overmarked. If you are in Cambridge and trying to go someplace 25 km away, this tagging is not helpful. If you are trying to get someplace in Cambridge, it makes a lot of sense. I think what's really going on is that there is a bigger hierarchy of roads than our present categorization supports. If you took Cambridge and downgraded all the tertiary to quarternary(!) and then 80% of secondary to tertiary, it would seem about right. I think people tagging in cities want (and need) a category for roads that are of local importance within a neighborhood that's only 1-2km across. The alternative is to redefine 'gets you to the next big area' in terms of population, but I really don't like that. I realize also that I'm influenced by the layout of Mass, with colonial town centers just close enough that everyone could walk to church. But I think tying to national-level roads as the baseline scales with living distance reasonably. Google maps seems to merge the primary/secondary and not have tertiary. While it doesn't look overmarked, it's also less useful and gets importance wrong: http://maps.google.com/?ie=UTF8&ll=42.366028,-71.113214&spn=0.044201,0.094585&z=14 http://maps.google.com/?ie=UTF8&ll=42.43524,-71.490&spn=0.088305,0.189171&z=14 I'm also very curious about what those that have actually studied cartography think of all this. There's a lot of established wisdom and practices and I think we're as a community too much in the 'ignore history and roll our own' direction.
pgp8qjtmWLzdm.pgp
Description: PGP signature
_______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
