Why and how

In Slovakia we have electronic cadastre available and it contains buildings in vector format with building conscription numbers (in our country it is conscription number Key:addr:conscriptionnumber ). These information are public and we have some smart OSM users that created a conversion possibility to get it into OSM maps KaporSKAddress#Conscription_numbers_import .

I have decided that I will use available method that takes cadastre house numbers and assign them to OSM map buildings in my town and then I will verify how correct these data are. Goal was:

  1. have houses with numbers searchable in OSM. It was found to be helpful also for ambulances in case of emergency to have searchable map!
  2. to keep OSM map up to date - to reflect reality which is goal of OSM
  3. by curiosity to see how precise are cadastre data

My town has approx. 1600 inhabitants and 632 houses plus some garages, cottages and huts. Town has approx. 10 streets.

Fast part

Building shapes are already imported into OSM for most of Slovakia for some time. Though, importing conscription numbers can’t be fully automated and it can be tricky. Jose helped me with import process (thank you!) and it took less than half a hour; This was the first commit.

Slow part

Import process shown that in about 15 cases different houses had the same house number. I decided to resurvey whole village to verify all the house numbers (because of reasons 1-3 above).

So I have printed out zoomed OSM map with visible building numbers on paper. I walked around the town and noted down if something was not correct (I have done this in 4 separated sessions). After each session I started JOSM and corrected houses that needed correction, removed ‘import notes’ from houses, added source:conscriptionnumber.

My findings

  • I had 4 walking sessions around the town, each took me about 1,5 hour and fixing the data in JOSM was another 30-45 minutes. That sums up to 8-9 hours for my small town!
  • 73/632 of houses did not have visible numbers on the house
  • 10/632 houses were not reachable to verify their number - they were inside locked yards, and number was not on the gate either
  • 26 houses look like a real house with families living for some time inside, but they have no number in cadastre or on the house
  • ~5% of houses in cadastre data were somehow wrong - incorrect number, two houses had the same number (either completely different houses or two joined buildings, sometimes one of them is garage)
  • it is not good to do paper-walk mapping in cold weather, your fingers freeze off :)
  • people stare at you if you are looking on buildings and note something into a paper sheet :-)

I have realised that after 4 walking sessions I am still missing some data and had to make 5th, and yesterday I was checking all the data if they all have a proper source:conscriptionnumber and I realised that I’m still missing that on 30 buildings and I need to make 6th walk.

What would I do differently next time

  • do walking sessions while it is summer and you can feel your fingers, otherwise you will need to wait for next warm season
  • print out walking papers in good detail and think if there will be enough space to write comments on walking papers
  • write real comments on walking papers, not just abbreviations, you forget those abbreviations if you upload the data after few days
Location: Cigánska ulička, Sološnica, District of Malacky, Region of Bratislava, 906 37, Slovakia

Comment from SK53 on 25 August 2016 at 14:20

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.

Comment from alexkemp on 26 August 2016 at 02:38

Hi @MiroJanosik

You write: “do walking sessions while it is summer and you can feel your fingers”. Um, isn’t it Summer in Slovakia right now?!

Mistakes: we are human, try to put up with it whilst you learn. I found myself having to redo all the time, but slowly I got better.

An hour for each street sounds about right. It takes a terrifying amount of time to survey on the ground.

Comment from MiroJanosik on 26 August 2016 at 10:38

Hi @alexkemp » Um, isn’t it Summer in Slovakia right now?! Yes, summer is here now. To explain - I have started with this survey on the end of summer of 2015 and then I could not continue because of cold weather, so I had to wait until summer 2016.

Comment from Nakaner on 30 August 2016 at 19:53

MiroJanosik wrote: > it is not good to do paper-walk mapping in cold weather, your fingers freeze off :)

You should buy a hybrid glove. I use them for mapping and professional surveying (as a surveyor).

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