OpenStreetMap

Landuse and highway sharing

Posted by Dashers on 13 February 2014 in English (English)

This is an age old-debate: How should one marry up a landuse boundary and a road? Should, with the convenience of Bing Maps, we try and map the land use up to the edge the road on the image - or just connect it up with the road.

Initially when I started mapping I took the former approach, and kept things split. It wasn't until I had noticed somebody had mapped the pavement (or sidewalk for you yanks) along side a road in one village that I started to realise the error of my ways.

Landuse - is just that. The designation of the land - often this is split up by highways (roads and rivers etc). The issue we have is that the line on the map editor is one dimensional - there is no width information, so when we zoom in, the land use edge appears to end in the middle of the road. This is an easy mistake to make as it is what we see but we have to remember when the map is rendered, the road has a width to it and it is entirely sensible for the road to be the dividing section of different landuses.

The alternative approach would be to draw roads as areas themselves, defining the landuse as highway. This of course is a silly idea.

The messy bit arrives when there is another border for the landuse and road - in the form of a hedge or fence. This then gets confusing - where do you stick the hedge? If you stick it in the correct place then usually it's drawn over by the road when it renders. You can't join it on the highway node though, as there are usually a barrier on both sides of the road - and the highway is one-dimensional. Conundrum.

Whilst highways can already have the width defined, I don't think it's something that is really supported or widely used. I think perhaps in addition to this we need to think about having attributes that relate to the edging of roads - this could quickly get complicated though - what about where only one direction has a pavement? What if it has a pavement and a fence?

Comment from RobJN on 13 February 2014 at 18:43

You can tag a pavement on a highway by adding sidewalk=both/left/right/none (as appropriate).

http://wiki.openstreetmap.org/wiki/Sidewalk http://wiki.openstreetmap.org/wiki/Forward_%26_backward,_left_%26_right

As for landuse, I prefer to map up to the edge of the road but not join it to the road. In UK rural areas, I will mark farmland up to the hedge (the small grassed areas between hedge and tarmac are almost always maintained as part of the highway).

Rob

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Comment from Dick Tecktiv on 13 February 2014 at 18:54

The maps are useful to find our way and to locate things, no one will use it to measure the fields with an 1 square inch precision. In my opinion it is better to blend close lines, since it reduces the number of point and lighten the map.

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Comment from chillly on 13 February 2014 at 19:17

The way that describes a road describes the centre-line of the road. Beside the road there could be a verge, a footway, fence or hedge and then the adjoining property. Where would you put these if you have (wrongly in my view) joined the property beside the road to the centre-line of the road? Later editing of detailed infrastructure is a real pain if you have to split the road from landuse. You can add an area around the road as landuse=highway, similar to landuse=railway, to describe the highway land that is not the adjoining property.

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Comment from SK53 on 13 February 2014 at 19:22

@chillly +1

@Dick Tecktiv: WRONG. OSM data are used for analytical purposes, for instance the length of hedgerow in farmland is a good parameter for assessing the lands suitability for nesting habitat for birds. Most landuse will assign a landuse/landcover type of highway to encompass the road surface and its wider corridor (verges, pavements/sidewalks) etc. If your bring landuse to the road centre line then it forces people to make approximations for the areas used by the highway. What you suggest simply does not take account of the multitude of different things OSM data is used for.

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Comment from Dick Tecktiv on 13 February 2014 at 20:06

A fence is ok to be off the road, but it can be blended with the border of the property. A footway is a different track, I never told him to stack tracks. For the analytical purposes, you just have to fill the tag counting the number of lanes, and if it were so important everyone would have already done it. For the birds, even by separating all the lines, the map is accurate in very few places. Farmers would use fieldworks or Google street view to assess the distance between the roadside and their field. And to measure surfaces, the scarce countries where OSM coverage is completed have already measured the parcels of land and recorded it in a land register.

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Comment from SK53 on 14 February 2014 at 10:49

Farmers in the Western world these days are much more likely to have extremely accurate GPS which is used to determine exactly where to add fertiliser.

You make far too many assumptions about land registers, and anyway a lot of this data is not available, or very costly, in many countries (the whole reason OSM started in the first place).

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Comment from Dashers on 18 February 2014 at 12:10

I think chilly has a good idea of landuse=highway, this though is not yet a supported tag and ultimately I think this is the only way to unify the one-dimensional concept that is a highway in OSM and two-dimensional landuse areas.

There are a number of users I note that will use bing or GPS mapping information to define boundaries as well as a few arguments in these comments to using this data for accuracy - unfortunately this is just a fallacy, this information is not precise. Even if precise information could be obtained it does not address the dimensional mismatch. Some users are going round and unlinking ways (very annoying) with comments of "removing from road-centreline", which again just doesn't make any sense as the concept of "centre" means two dimensions.

We also get into the sticky situation of mapping landuse over property boundaries. A residential area will have roads through it, the conversation above relates largely to the final edge before the landuse changes and whether it is sensible to use the road as a defining barrier. I think this is entirely acceptable - the land use is residential up to the road line, but the property boundary may end earlier with a fence or something.

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