SK53 has commented on the following diary entries

Post When Comment
Adding house numbers of one town from cadastre to OSM and survey verification 8 months ago

This sort of careful comparison of official data and what is on the ground is very useful. The fact that there are errors in the official cadastral data is not surprising (I once bought a house which had the parcel mapped incorrectly), but a good estimate of the extent of the error really helps in evaluating just how useful any given import is likely to be.

Equally really good OSM data does require revisits to check things and collect data which one has missed. This is the only way we can try to have data which is even better than the official sources.

Nottingham's Mysterious Plaster Boys & Girls 10 months ago

and I got the name from a Geograph photo by Alan Murray-Rust

Nottingham's Mysterious Plaster Boys & Girls 10 months ago

I suspect their core is rather more solid than plaster. I did document the tag on the wiki:

Don't Mention the War 11 months ago

Yes, also interesting that a house on Ribblesdale Road (Sherwood N of Valley Road) was bombed. It ought to be possible to pick it out, but many houses have been substantially extended in recent years (when I surveyed it in 2011, there seemed to be builders everywhere).

There ought to be more details of the bombing somewhere: Local Studies Library or Notts Archives perhaps. Both the Nottstalgia thread & Dominic Morrow's recent blog post about the Nottingham Canal make me intrigued about the location of air raid shelters in WWII.

One other point mentioned in one of your earlier posts was Robert Mellors : I presume this is the same person who wrote "Nottingham Suburbs Now and Then" (e.g., Basford) in the early 1900s.

Don't Mention the War 11 months ago

You're not the first to come across this phenomenon on the E side of the city: there's a new house inserted in one of the side roads in Sneinton Elements: see WWII Bombs in Nottingham.

The wikipedia has a useful map of bombed locations:

Nottingham Blitz

Trees (again) about 1 year ago

I'm sure that there are fairly standard cartography symbols for recently felled woodland: usually in the form of a tree icon on its side. I've had a go at these before. but not very satisfactorily. Currently I tag these as recently_felled=yes or with year of imagery.

As BushmanK says it may be more appropriate to keep filled/unfilled symbology for deciduous/evergreen. The long discussion about 'unknown' woodland type sort of agreed for the double symbol (mixed woods would have a 50/50 split of single symbols).

Many thanks for drawing @igitov's suggestions to my notice. These do look pretty sensible. I'd probably prefer woodland over wood as the principal 'namespace').

Help map some sidewalks for cities in the U.S. about 1 year ago

Hi Martijn,

sidewalk=none is the most used value when sidewalks are not present on either side of the road, not sidewalk=no. It would be nice if we avoid creating two equivalent values.


Are most subway stations actually railway=halt? about 1 year ago

Places which I'd consider to be halts in Switzerland include a number of stations on the RhB. Obvious ones are:

  • Trin : unmanned, trains only stop on request. The standard station building is now a private residence.
  • Acla de Funtuana : mainly useful as it is closer to the cable car than Disentis station. Not much there from memory.
  • Celerina Staz : not much used.

These are all on single track lines, and generally the RhB always has switches & more than one track in stations: it's the single thing which ensures resilience in the system.

Other lines where stations might likely fit the UK notion of a halt are:

  • Golden Pass line
  • Line from Delemont to Le Chaux-de-Fonds
  • Numerous mountain railways (Rigi, Brienzer Rothorn, Rocher de Naye)

In the UK there are some halts in odd places:

  • Furze Platt : a single platform on a branch line with a tiny ticket office manned on weekday mornings. Otherwise no station buildings.
  • Marlow : this used to be a proper station, and although it's the terminus now has about as much infrastructure as Furze Platt + a ticket machine.

Many of the stops on the lines in Mid Wales & the Highlands of Scotland would also fit the notion of halts. As would Lakenheath which is not only a halt but has about 1-2 trains a day.

I would presume that the canonical halt was Adelstrop.

Finally, what defines a halt, typically some or all of the following:

  • Low to very low passenger volumes
  • Infrequent train services
  • Single track line
  • Absent or reduced normal station infrastructure (buildings, ticket office, waiting rooms)
  • No or very limited staffing
  • Trains only stop on demand
  • On a branch line

To which we can also add the no switches, but ultimately I think the definition of halt must reflect the fact that a halt is somewhere a passenger would expect to find none of the usual services.

As most of my examples above are probably tagged railway=station this distinction may not be that useful on OSM. I would certainly strongly advise against retagging metro stations as halts.


Showing off surface tags about 1 year ago

A real quickie: you can write rules of the form surface in ('asphalt','concrete'....), easier than lots of ORs. There are probably quite a few other QGIS tips which might help.

Starting around my local area about 1 year ago

It's quite likely that many POIs (post offices, places of worship, schools etc) came from the Geographical Names Service (GNIS). These are rarely located accurately (anything from a couple of blocks to a couple of counties out): a real bonus is when someone locally can improve these locations. Good hunting.

Birding Spots of Bangalore about 1 year ago

Do tell more. Would be interested in sharing experiences about what is useful to map for birders.

Mapping small / lesser known businesses in Slums of Mumbai about 1 year ago

If these are small shops or small craft workshops then tag them as such. It would be an excellent exercise to have one or two such places mapped in detail: only in doing so does one discover exactly what might need to be tagged.

I'd slightly take issue with the idea that selling good through a middle man is outdated. Many OSM contributors in North America & Europe, likely sell their labour exactly that way as contractors in IT industries. Certainly friends who run craft shops in Britain also need the middle men to provide them with work when tourists aren't around during the winter.

Direct selling can often be much more expensive than using intermediaries, and particularly so for smaller businesses, but I applaud your sympathy for these folk. It's worth talking to some of them: I think you might be surprised how well they know the marketplace they are in. Certainly I've had some really illuminating conversations with people running fast food outlets and local stores in the UK whilst out mapping.

West Street Blues over 1 year ago

If you use a North America-based Garmin extract this may well happen!

I doubt it this applies to the most widely used UK-based extract (that by Talky Toaster).

UK addresses are a well-understood issue: they require diligent on-the-ground surveying. To say this is not everyone's cup of tea, would be an understatement. The main result of an open address initiative was to place under suspicion our biggest potential source of open address data: so whereas 18 months ago it looked like a lot of basic data could be developed semi-automatically, we're back to where we were before.

For several years I have been advocating using the Food Hygiene Open Data to add address data to already mapped POIs as a way of bootstrapping post codes and addresses.

Cleaning up NHD in North Carolina over 1 year ago

@bdiscoe: no problems, its meaning was fairly obvious. As for canal/ditch in W US: this is a real mess. We also don't have sensible ways of separating an irrigation channel which is a foot wide from massive 60-100 foot ones, and those from canals for boats. My impression is most of the CO ones I little more than cut & cover channels of a few inches/feet; but one cant see anything on aerial imagery & therefore tends to the (false) presumption that NHD data knows what its doing.

I played a bit with a random area in the Upper Colorado Basin, where the data isn't quite as insane as in NC, but just a quick random edit stripped a few thousand nodes out of the imported NHD data.

Cleaning up NHD in North Carolina over 1 year ago

This is a really useful discussion.

I remember trying to tidy up bits of this data around Wrightsville Beach and giving up. It didn't help that my memory of what was there is rather fuzzy, but it was quite clear that some wetland features just shouldn't have been there. I suspect most of my cleanup was just node de-duplication. Certainly I did enough of that sort of thing to write-up my process. I think EdLoach used this idea tidying up Georgia landuse until someone objected.

Looks like I need to run over the Colorado Basin data too, also complicated by intermittent watercourses.

Lastly, I'd not come across the term "decimation" applied in this way before: obviously it's a GIS term. Not all of us have that background, although its fairly understandable after the second or third reading.

Hadjer Lamis, Chad - Tracing guide over 1 year ago

An exemplary description of detail needed for intelligent remote mapping. The availability of photographs and on-the-ground descriptions (as well as a round up of the more typical gotcha's) should help everyone. Furthermore I think a lot of this description can be useful for many other parts of rural Africa, and even Asia. (It wouldn't do any harm to have such descriptions for Western cities either)

It may be useful to explicitly tag tukuls in some way. I vaguely recall thinking about this with mokhoros in Lesotho, and indeed over 9000 have been tagged explicitly and a few more with building=hut, hut=mokhoro. Personally, I have some reservations about building=hut for dwelling places, but can't think of a better alternative. Certainly it is better to use a generic tag than to have tens of regional names for small circular thatched buildings built from local materials, whether tukuls, mokhoro, or Sindhi round houses. One other thing I have wondered about such buildings is what materials are used for thatch, and whether its is possible to map where such resources are located.

Mapping my hometown Rajahmundry over 1 year ago

@Warin61 is quite right, but the imagery alignment problems are very daunting for the mapper.

As @SimonPoole says getting some useful alignment traces really helps. In the past mappers in India without access to a smartphone capable of recording GPS traces have managed this by borrowing such a phone from a relative for an hour or two. Otherwise if you have a GPS-enabled phone an app such as GPS Tracker can be used.

Open spaces such as parks, temple precincts, wider highways are good places to try & capture decent GPS traces. Ideally you want a few as an individual trace will be affected by day to day vagaries.

There are a limited number of Strava tracks available in the area, but at least these can be used immediately:

You also may like to use an editor which uses the Imagery Offset database, which at least would allow the same offsets to be used consistently.

I would like to echo others comments that this is a nice write-up.

Units in OpenStreetMap over 1 year ago

The place for a cleaner database is not the main OSM API DB which mappers contribute to, but as a separate database where tag values can be normalised, additional values added (for instance higher-level categories, perhaps multiple versions of ways with different degrees of simplification etc. At the moment all these things happen but in application specific databases (such as the osm2pgsql format & numerous routing formats including your own),

I think one or two people have tried this (e.g., OpenCageData), but as a community type activity it would run into precisely the issues the current data has: who selects the values & transforms. Normalisation of data structures is even worse: many things tagged in OSM look quite simple on the surface, but often turn into really complex data modelling issues if one wants to formally capture all the nuances of what is tagged (I have a 30+ entity model to encompass what gets added to post boxes & I haven't even added anything about collection times which are at minimum a similar order of complexity again).

I also don't think we're ready for it either. Your own example probably demonstrates that the number of height & weight restrictions actually mapped in the US is a drop in the ocean compared with those that exist. Only when significant numbers are mapped does the tagging tend to coalesce around more consistent values. My best guess this is occurs when around 5-10% of actual things have been mapped.

BTW: I would love to be able to tweak Graphhopper without having to code Java, in exactly the sort of ways RIchardF describes. I also appreciate that GH may have the same issues with respect to number of developers as OSM editors.

Units in OpenStreetMap over 1 year ago

This is a really old discussion. When I first started contributing to OSM many speed limits in the UK were in metric units (I hesitate to call kph SI): no 30 mph, but 48.##, or 50 because it was easier. Guess what, folk couldn't be bothered to map speed limits, too complicated.

Maxheight in Britain is usually expressed in both feet and inches & a metric value: but the conversion used involves rounding. I believe there are some older rarely used places with only the older signage. Thus in this case both values should be tagged.

The last point is that over time there is a tendency to not just do the transformation (a speed limit sign to a speed limit on a road section), but also to map the actual original information (the sign itself). I think it was the Finns who first developed this idea. It greatly assists in checking for errors and for validating existing data. If units are converted it becomes much harder for someone to check that such data is correct: and don't ignore the likelihood that people will use approximations, perhaps to come back later when they've found a conversion formula.

As SomeoneElse said in the changeset comment: preprocessing out-of-band values is essential. You have to do it on data coming from databases with reasonably sensible constraints, so its unavoidable on data which is free text. Only today I've been processing postcodes and apart from partial values, garbage in the string etc, there have been several telephone numbers. Of course a nice thing is if one can 'close the loop': inform the contributor who generated those values in the hope that they will correct/improve them.

In summary: asking for contributors to do more will probably cause them to do less.

Quantifying HOT participation inequality: it's complicated. over 1 year ago

I miss the detail of how you derive the labour hours for contributors. If I edit offline in JOSM and do not sign-up via the Tasking Manager how do you know how long I spend on my edits? Many experienced contributors to OSM will tend to prefer their personal workflow to that imposed by TM.

Other well known factors contributing to these phenomenon in extreme citizen science (following Hakaly's terminology) activities are:

  • Skills. Contributors have different skill levels. In this context core skills will be: familiarity with OSM editors, interpretation of aerial imagery, familiarity with OSM tagging, personal workflow. In many domains those who have mastered core skills can result in 10-100 fold greater productivity compared with those who haven't: but particularly true in citizen science context.
  • Triage. Some contributors may focus better on the easy to map important stuff rather than trying to complete a square. My impression is that proportionally a lot more effort will be spent on the final stages of square completion than earlier phases. I would expect this to also show a Pareto curve.
  • Early Mover advantage. A skilled experience contributor practising triage may map a much larger percentage of the easily mapped things in a particular area if they start contributing at an early stage in the project. This was certainly true of Haiti: it was quite hard for newcomers to find something useful to contribute around Port-au-Prince within a few days. Another factor in this is its much easier to draw a road network on a blank area of the map.

I suspect that on-the-ground experience cuts both ways: it eases interpretation, but at the same time inhibits mapping stuff known to be more complex than imagery allows.