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#1 2020-11-18 19:50:37

osm-sputnik
Member
Registered: 2020-06-07
Posts: 6

Boundaries in Crete - Some problems

Hi everybody,

Back in June I was preparing an exposure model for Attica. This model is describing all buildings and their vulnerability to earthquakes. During this work, I have discovered several little discrepancies between OSM boundaries and the GADM (www.gadm.org) and data from https://geodata.gov.gr/en/dataset/oria- … allikrates. After posting this here, the problems were fixed really quickly.

I'm now expanding the model to all of Greece and therefore I'm checking all boundaries of the admin_level=7 districts. I started with Crete and I found again several discrepancies for which I'm not able to find any confirming information in English:

Case 1: Paximadi

Does Paximadi island belong to Chersonisos? It is currently not assigned to any district (admin_level 7). GADM considers this island to be part of Chersonisos as does geodata.gov.gr.

https://www.openstreetmap.org/relation/873461

Case 2: Glaronisi

Does Glaronisi island belong to Chersonisos? It is currently not assigned to any municipality. GADM and the geodata.gov.gr municipality boundaries (Kallikratis and Kapodistrian) also do not consider this island to be part of Chersonisos.

https://www.openstreetmap.org/relation/873060

Case 3: Agii Pandes and Mikronisi

Do Agii Pandes and Mikronisi islands belong to the Agios Nikolaos district (admin_level 7)? GADM considers this island to be part of Agios Nikolaos as does geodata.gov.gr.

Agii Pandes: https://www.openstreetmap.org/relation/855217

Mikronisi: https://www.openstreetmap.org/relation/890547

Case 4: Vryonisi

Does the island of Vryonisi belong to the district of Agios Nikolaos (admin_level 7)? GADM and geodata.gov.gr considers it to be part of Agios Nikolaos.

https://www.openstreetmap.org/relation/891599

Case 5: unnamed island

According to geodata.gov.gr, this unnamed island should belong to the Agios Nikolaos district (admin_level 7) but it is currently not assigned to any district at the admin_level 7.

https://www.openstreetmap.org/way/505334728

Case 6: unnamed island

According to geodata.gov.gr, this unnamed island belongs to the Ierapetra district (admin_level 7) but it is currently not assigned to any district at the admin_level 7.

https://www.openstreetmap.org/way/505334661

Case 7: Psyllos

According to geodata.gov.gr, the island of Psyllos belongs to the Ierapetra district (admin_level 7) but it is currently not assigned to any district at the admin_level 7.

https://www.openstreetmap.org/relation/892922

Case 8: Konida

The island Konida is assigned to the municipality of Kavousi but not to the district of Ierapetra (admin_level 7). According to geodata.gov.gr, it should also belong to Ierapetra.

https://www.openstreetmap.org/relation/894390

Case 9: Agriomandra

The island Agriomandra is assigned to the municipality of Kavousi but not to the district of Ierapetra (admin_level 7). According to geodata.gov.gr, it should also belong to Ierapetra.

https://www.openstreetmap.org/relation/895148

Case 10: Katergo

The island of Katergo is only assigned to Lasithi regional unit (admin_level 6) but should, according to geodata.gov.gr, be also part of the district of Ierapetra (admin_level 7).

https://www.openstreetmap.org/relation/895666

Case 11: unnamed island

According to geodata.gov.gr, this unnamed island belongs to the Ierapetra district (admin_level 7) but it is currently not assigned to any district at the admin_level 7.

https://www.openstreetmap.org/way/223332259

Case 12: missing islands (rocks)

According to geodata.gov.gr, there are a couple of islands (or rocks) that belong to the district of Ierapetra (admin_level 7). The islands show up on Bing and Google satellite imagery but are not included in OSM.

https://www.openstreetmap.org/?mlat=35. … 4/25.86058

Case 13: Grandes West and East islands

The Grandes West island belongs, according to geodata.gov.gr, to the district of Sitia (admin_level 7) but it is currently not assigned to any district at the admin_level 7. Geodata.gov.gr is not assigning Grandes East to any district. Is this correct?

Grandes West: https://www.openstreetmap.org/relation/896167

Grandes East: https://www.openstreetmap.org/relation/896166

Case 14: Anavatis, Kavallos, Kefali islands

The islands of Anavatis, Kavallos, and Kefali belong, according to geodata.gov.gr, to the district of Sitia (admin_level 7) but they are currently not assigned to any district at the admin_level 7.

Anavatis: https://www.openstreetmap.org/relation/896171

Kavallos: https://www.openstreetmap.org/relation/896170

Kefali: https://www.openstreetmap.org/relation/896172

Case 15: Kymo

The Kymo island belongs, according to geodata.gov.gr, to the district of Sitia (admin_level 7) but it is currently not assigned to any district at the admin_level 7.

https://www.openstreetmap.org/relation/896175

Case 16: boundary between Sitia and Ierapetra districts

The boundary between the districts of Sitia and Ierapetra at the admin_level 7 is very different from the same boundary on geodata.gov.gr (the Kallikratis boundary). Geodata.gov.gr and GADM show essentially the same boundary line (see also the boundary on https://en.wikipedia.org/wiki/Lasithi). The boundary in OSM is composed of the two relations

Sitia: https://www.openstreetmap.org/relation/2187435

Ierapetra: https://www.openstreetmap.org/relation/2187433

I would be grateful if somebody can help me with confirming or fixing the cases 1-15. I'm happy to fix them myself, however, I don't feel comfortable to change boundaries in Greece without consulting the community first as my sources to prove anything here are limited and I don't understand the copyrights on Greek websites.

If cases 1-15 are not fixed or cannot reasonably be fixed, this would not be a problem as all these little islands seems uninhabited and there will no measurable consequence for the model. However, case 16 is very different: the boundaries in OSM and geodata.gov.gr are many kilometers apart and truly covering different areas. Can somebody explain this discrepancy?

Thanks a lot for your help!

Cheers from Berlin, Germany

-danijel

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#2 Yesterday 01:44:51

jimkats
Member
From: Greece
Registered: 2020-06-02
Posts: 9
Website

Re: Boundaries in Crete - Some problems

Hello danijel

Sorry for not responding on time. I viewed these 2 topics when you posted, but I was dealing with other stuff tongue

The main reason why some islets, all over Greece, don't have any or not all proper boundary relations is because, in my opinion, previous people didn't bother or forgot to add. From what I see, current mappers from Greece aren't many, as in other countries, so the mapping process for anything related with boundaries is slow.

I happen to have started recently (since October) a personal project of adding and fixing those administrative relations all over Greece (I may be the only one currently doing that, so masochist tongue). My main focus is municipal units (admin_level 8). But if I see an easy opportunity, I add any missing boundary, because like half of Greece misses the lowest-level boundaries (admin_level=9 for communities/communes). Not to mention the wrong terms used in the localized names, like in Ierapetra (admin_level 7) for English was written as District, although it's actually Municipality (just fixed it).

I also saw few cases of various boundaries discrepancies, not only between OSM and geodata, but even in geodata itself. I can't understand why this happens in geodata, but my guesses are about what local governments provided for boundaries when the datasets were created, different in each time. Because like in most places, local actual boundaries are vague.

Personally, when I was drawing some boundaries recently which were different in geodata (using datasets of pre-Kapodistrias plan and of Greek Statistical Authority), I searched online for any maps or reference to those boundaries and tried to see what looked like official, recent and most used (in relation with other maps).

I haven't seen yet the issue you mentioned about the many kilometres difference, but I may look at it in the near future (my mapping schedule based on mood :d). Sorry if this post didn't answer in what you asked, but if you need anything contact me via PM in OSM smile

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