Hi Folks, recent I have been going over parts of OSM mapped some time ago, following up on the infamous redaction. One thing that jumps out at me is the inconsistent tagging of dirt roads. Even, I must say, ones I have done myself but over a several year time span.
So I started to write some notes for myself and thought that maybe I should add them to http://wiki.openstreetmap.org/wiki/Australian_Roads_Tagging I don't think this is inconsistent with whats there now, just more detailed. However, I do suggest that we need consider what the rendering engines do with our data and I know that is a bit naughty. But, in this case, I'd suggest to do otherwise is negligent as it can have quite serious safety issues. So, would people like to comment on what I say here ? If we can reach consensus, I'll graft some of it onto the OSM wiki. Unmade roads These are typically forestry and remote tracks, while they may have been cut initially by a bulldozer they are not regularly maintained and, importantly, are not domed and don't have good run off gutters on the side. Such roads might or might not be single lane, 4x4 only, might be dry weather etc. Be careful about deciding on such restrictions, some people are often surprised at how well a carefully driven conventional vehicle can use these tracks. Highway=track will typically render to a dashed line. highway=track surface=unpaved lanes=[1; 2] 4x4_only=[recommended; yes] source=survey Made but unsealed roads. Many rural roads fit here. There is no asphalt but the roads are 'made' and regularly maintained by, eg, the local council. These roads often have a gravel base, always have dome shape, the middle is somewhat higher than the sides and there is some sort of gutter at the edge. The gutter will usually have "run offs" to drain water away from the road. Such roads are almost never 4x4_only nor dry weather only. highway=[unclassified; tertiary, secondary] surface=unpaved lanes=[1; 2] source=survey Use of the highway tag on dirt roads. While the selection of tags should not be defined by how current rendering engines display, we cannot ignore the final outcome. In Australia, a lot of dirt roads are quite important and sometimes its necessary to compromise a little to achieve a useful result. So the correct highway tag may be determined by a combination of the purpose of the road and its condition. Tracks are often rendered as dashed lines and most people would understand that means some care may well be needed. Unclassified would indicate a purely local function and is typically rendered as two thin black lines with white between. Tertiary roads usually are rendered with two black lines and a coloured fill and many people (incorrectly) interpret that as meaning a sealed road, so maybe mappers should ensure they apply that tag only to dirt roads that are reasonably well maintained. Secondary roads are shown as wider and a different colour than tertiary and are definitely presented as viable routes for people passing through the area. Some care needs be exercised if a dirt road is to be classified as 'secondary'. Discussion Sometimes its hard to balance the description of a road against its purpose. A good example might be the Plenty Highway. This road is probably a track from a road condition perspective, rarely maintained, sections of sand, corrugations and ruts. However, its pretty long and a major link between some (admittedly small) communities. As a 'track' it would not show up on a map until you zoom in way past where you can get any idea of where it starts and ends. At time of writing, its highway=primary (and, I might note, incomplete), that's possibly dangerously misleading. Conventional vehicles routinely use it but I'd probably give it a 4x4_only=recommended tag. However, none of the mainstream rendering engines observe that tag, it is no real protection for a visiting tourist. Similarly, even on the east coast, its not unusual to see dirt roads defined as 'tertiary' or even 'secondary'. Thats probably quite correct from a purpose view but a lot of (especially city based) drivers get quite nervous when they find themselves on a dirt road. If they have got there by following a OSM map showing a road with coloured fill, maybe they have a case ? Most printed maps here in Australia show unsealed roads without a coloured fill. And this does, of course, highlight the need to survey roads. David
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