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Triskaidekaphobia in the USA

mer 25 aoû 2021 - 13:25

Reading DeBigC’s diary entry on Triskaidekaphobia in Dublin reminded me that I had also looked at the same thing in the USA. The US Department of Transportation (USDOT) has a National Address Database containing about 60.5 million addresses from which we can plot the frequency of street numbers in the range of 1 to 19:

Cities and Villeges

mer 25 aoû 2021 - 12:10

Aurangabad, Mumbai, Pune, Nagpur, Ahmednagar, Nashik, Dhule, Nandurbar, Shirur, Akole, Bhandardara, Sangamner, Shrirampur, Nevase, Bodhegaon, Shevgaon, Balamtakli, Beed, Ambajogai, Latur, Ghargaon, Badgavhan, Chaklamba, Mungi, Chapadgaon, Nilanga, Udgir, Chikhali, Nanded, Makni, Dhanora, Tulajapur, Chakan, Phopade, Khori, Bhopal, Bengaluru, Hyderabad, Delhi, Kolkata, Varanasi, Ellora, Ajanta, Devgad, Satane, Chakur, Chakan, Satara, Loni, Gangapur, Vaijapur, Kasoda, Ambelohol, Bhalgaon, Chitegaon, Dhorkin, Beedkin, Ichalkaranji

Cómo corregir nombres, como la palabra río (a partir de rio)

mer 25 aoû 2021 - 7:09

En Colombia, los ríos tenían diferentes palabras para la palabra Río que hace parte del nombre. Sin embargo, hacer esta modificación de cada way no era viable, por lo que lo hice de una forma masiva. Aquí muestro los pasos para replicarlo:

  • Buscar el nombre de departamento o región a analizar, para no hacerlo masivo sino por partes.

[out:xml]/*fixed by auto repair*//*fixed by auto repair*/[timeout:25]; area[name="Colombia"][admin_level=2][boundary=administrative]->.searchColombia; area[name="Amazonas"][admin_level=4][boundary=administrative]->.searchDpto; ( way["waterway"="river"] ["name"~"^(Rio|rio) "] (area.searchDpto)(area.searchColombia); ); (._;>;); out meta;/*fixed by auto repair*/

  • Revisar que los ríos quedan dentro de Colombia, ya que si son fronterizos no queremos hacer cambios fuera de la jurisdicción. Para esto se ven los resultados de overpass turbo en el mapa.
  • Si quedan fuera de Colombia, editar los ways individualmente para que solo tome lo de Colombia partiéndolos justo en la frontera.
  • Exportar los resultados del query de Overpass Turbo a JOSM.
  • Una vez en JOSM, seleccionar todo, Ctrl A.
  • Abrir el filtro para solo seleccionar los ways Ctrl F.
  • Indicar en la ventana:

selected type:way

  • Adicionar una etiqueta para que modifique todos los ways. En mi caso puse esta:


  • Guardar los datos como rios.osm
  • Borrar la capa modificada.
  • Desde una terminal que tenga sed (Linux, Max, cygwin, mobaxterm en Windows) hacer el cambio masivo por medio del comando Sed.

sed "s/tag k='name' v='Rio /tag k='name' v='Río /g" rios.osm | sed "s/tag k='name' v='rio /tag k='name' v='Río /g" | sed "s/tag k='name' v='río /tag k='name' v='Río /g" > riosmodif.osm

  • Abrir el archivo de nuevo en JOSM: riosmodif.osm
  • Actualizar datos - Update data Ctrl U.
  • Seleccionar todo Ctrl A.
  • Borrar la etiqueta andres=gomez
  • Subir datos. Si hay errores de validación, corregirlos.
  • Poner un nombre propio para este cambio.
  • Borrar la capa de datos.

2021-08-26 19:00 OSM Fonó: fotónézés Berekfürdőn, távsegítség (online)

mer 25 aoû 2021 - 0:13


mer 25 aoû 2021 - 0:00


Google Summer Of Code '21 Final Report for Element History Widget

mar 24 aoû 2021 - 10:50

I started google summer of code with the aim of creating a library that can be easily added to Vespucci and provide it with element comparison features, and provide some other feature requests in Vespucci. I was able to create and deploy the Element History Dialog, which can be found here, where you can find the implementation details for the library.

Work Done

The major work done during the coding period includes the following -

  1. Creating the parser for OSM elements
  2. Creating the parser for Changesets
  3. Creating the UI to list all versions for a selected OSM element
  4. Creating the UI for comparison between different OSM elements
  5. Logic for comparison between tags of different versions of a element
  6. Logic for comparison between data for 2 versions of a node
  7. Logic for comparison between data for 2 versions of a way
  8. Logic for comparison between data for 2 versions of a relation
  9. Handling edge cases like deleted elements and versions
  10. publishing the library and creating the sample application

A more detailed usage guide can be found on the github readme

Future Scope

Some additions to the project that I plan are -

  1. Creating more test cases - currently there are a few unit tests that test the basic functionality of the app, I will add more unit tests to cover most logical operations and few UI tests to test the basic flow of the library
  2. Adding the library to vespucci
  3. Creating Pull Requests on Vespucci for other features mentioned in my gsoc application.

Finally, I would like to say that my experience with the OSM community has been great, and I would love to contribute more to the great projects that are hosted by OSM

pos jaga

mar 24 aoû 2021 - 8:00


POI Dataset

lun 23 aoû 2021 - 23:28

I’ve been working on collecting datasets for various chains across the UK, and the globe. Yesterday I changed the repo to open, so say hello to KAFF Places. It’s mainly got retail chains, but it also some hotel chains, pharmacies and the like. You can see the list here.

This data is first party from their respective websites, interestingly enough there are a lot more quality issues that come with that than I expected. I have reached out to some of them to point out issues, and I’d love to work with all of them to improve their data.

I’m waving any database rights I may have, but because this is first party data each provider holds copyright and/or database rights. I currently do have some rules on which sites I collect data from, the most important rule is that they are publishing the data in Linked Data or Microdata. I personally believe once somebody explicitly publishes data in a machine readable format they want the data to be used. However the law may disagree. This shouldn’t be used as a source for OSM.

Some of this data is already being used by Robert Whittaker in Chain Reaction to help monitor the quality of OSM coverage. I’d also like to see this data being used as an overlay on top of OSM data to increase coverage in under mapped areas, in projects like OsmAnd and Daylight Map Distribution.

Triskaidekaphobia in Dublin

lun 23 aoû 2021 - 21:23

I map a lot of buildings in northern Dublin City. I also interrogate housenumber interpolations, view mapillary for little peeks of the housenumbers that aren’t blurred, and do my own StreetComplete captures to add as many address details as possible. Lately I have noticed something, born from a concern that I was doing something wrong, or making a mistake.

In a few housing developments around Dublin housenumber=13 doesn’t exist. I have heard of such indulgences before, for example some airlines dropping row 13 from seating plans, or the Irish car registration authority famously dropping its numeric system in 2013 to avoid the unluckiest of car numbers.

So out of curiousity I hit OverPass Turbo and launched a series of queries like this into the existing housenumbers. I couldn’t do loads of these so I thought that maybe 19 would be a sufficient sample (42,000 building objects) to make comparisons and establish patterns.

I plotted these values and observed, as expected, that number 1 is most frequent, since short streets and long streets all seem to have a #1. The numbers after #3 have a simple arithmetic decline. An unexpected result was that there are a few more #3s than #2s, but I will return to that in a comment if anyone wants to ask me :)…. Back to #13! There were around 60 less than I expected. This means #13 doesn’t appear so much as it should, even taking the decline in numbers and the finiteness of space for houses to be built into account.

I took this a stage further. I used an R-square test to establish if the quicker decline from #12 to #13, and slower decline from #13 to #14 are significant, in other words - is there something else going on with this blip in the decline pattern other than chance. And with an R-square value of .99 it seems there is indeed something going on!

All joking aside the lack of #13 may not be down to superstition, and may rest on a dominant architectural tendency to place an even number of houses on a site. It could be that mappers are superstitious, though I doubt it. So while this itself is not proof I give you Ashbook housing development in Dublin, where #12 and #14 are present but #13 is not.

Good Luck!

PS talk about this on twitter

Vespucci 16.0 Beta

lun 23 aoû 2021 - 20:23

Today we’ve started rolling out the 1st beta release of 16.0. If you intend to install this, or at a later date the release version, please read the release notes before installing.

Due to the preparation for targeting Android 11 there have been some changes in where files are stored that you need to know about.

zh-CN 的日記 / zh-CN ê Ji̍t-kì

lun 23 aoû 2021 - 8:50


最近毋知是按怎,近期的 zh-CN 日記出現誠濟篇指控 OpenStreetMap 無遵守中國的法律,竟然共台灣標示是獨立的國家。

臺灣人看著這款指控真無爽快,不而過猶是有精神來回應,是講 OpenStreetMap 的政策、運作方式佮精神,特別是爭議領土欲按怎處理的方式。

Pe̍h-ōe-jī ê pán-pún

Chòe-kūn m̄-chai sī án-chóaⁿ, kūn-kî ê zh-CN ê ji̍t-kì chhut-hiān chiâⁿ-chōe phiⁿ chí-khòng OpenStreetMap bô chun-siú Tiong-kok ê hoat-lu̍t, kèng-jiân kā Tâi-oân piau-sī sī to̍k-li̍p ê kok-ka.

Tâi-oân-lâng khòaⁿ-tio̍h chit-khoán ê chí-khòng chin-bô sóng-khoài, put-lî-kò iáu-sī ū-cheng-sîn lâi hê-èng, sī-kóng OpenStreetMap ê chèng-chhek, ūn-chok hong-sek kah cheng-sîn, tek-pia̍t sī cheng-gī léng-thó͘ boeh án-chóaⁿ chhú-lí ê hong-sek.

Tâi-lô ê pán-pún

Tsuè-kūn m̄-tsai sī án-tsuánn, kûn-ki ê zh-CN ê ji̍t-kì tshut-hiān tsiânn-tsuē phinn tsí-khòng OpenStreetMap bô tsun-siú Tiong-kok ê huat-lu̍t, kìng-jiân kā Tâi-uân piáu-sī sī to̍k-li̍p ê kok-ka.

Tâi-uân-lâng khuànn-tio̍h tsit-khuán ê tsí-khòng tsin-bô sóng-khuài, put-jî-kò iáu-sī ū tsing-sîn lâi hê-ìng, sī-kóng OpenStreetMap ê tsìng-tshik, ūn-tsok hong-sik kah tsing-sîn, ti̍k-pia̍t sī tsing-gī líng-thóo bueh án-tsuánn tshú-lí ê hong-sik.

Nominatim QA Analyser Tool - GSoC'21 Final Report

lun 23 aoû 2021 - 0:04

As we are reaching the end of the Google Summer of Code 2021, I would like to share with you the work done on my project “Nominatim QA Analyser”.

Previous diary entries Project summary

Nominatim is the OSM’s main geocoding software used to process geocoding requests on OpenStreetMap data. The software uses its own database schema which differs from the one used by the main OSM database. As a result, Nominatim processes OSM data in a way that allows to discover a lot of inconsistencies. The idea of the project was to build a Quality Assurance Tool which analyzes the Nominatim database and extracts errors from the OSM data based on a set of rules.

These extracted errors are then made available to everyone through a visual map, so that OSM mappers can correct them easily.

Running example

If you are curious about the result of the project, you can check a running instance here: It has up to date data which are generated by the backend analyser directly on the production server of Nominatim.

The web application will be set up on the official website later this month or early September. I will update the previously provided link in this diary entry when it will be done.

What has been done

The project is divided into two parts, the first one is the main Data Analyser tool which runs on the Nominatim’s server and the second one is the web application used to visualize the data through a map.

Data Analyser

The github repository of the Data Analyser can be found here: osm-search/Nominatim-Data-Analyser. The whole commits in this repository are from my work. You are free to contribute and help to make the tool better.

The development of this analyser includes:

  • A pipe based architecture developed in python with a YAML Rule Specification system used to easily add and customize QA rules. Learn more about this in the Mid-term project update I wrote.

  • The QA rules defined by @lonvia which are checked off in the following Nominatim issue: #1848 were implemented into the analyser.

  • A good documentation of the tool, available here.

  • About 95% of test coverage for the main python code.

  • Continuous integration has been set up in the github repository with github actions. It builds the tool and runs the tests for every push/pull request.

  • As a bonus, I had time to develop a custom C++ module to generate clusters based on a set of points data (in GeoJSON format) and then generate vector tiles from these clusters in the mapbox vector tiles format. This module is named clustering-vt and the code can be found in the Nominatim Data Analyser github repository. I used mapbox/supercluster.hpp and mapbox/vtzero as the main libraries for this module. And I can say that they are amazing libraries. We initially used Tippecanoe to generate the vector tiles but I wasn’t satisfied with the results we had. I wanted to use Supercluster so I developed clustering-vt.

Web application

Initially, we used osmoscope-ui as a website to display the data extracted by the analyser. Later in the project, I wanted to switch to a custom web application which allows us to have custom UI, features and side information. This was made a lot easier because we kept the layer definition of osmoscope.

This web application is developed with React. The code can be found here: osm-search/Nominatim-Data-Analyser-Frontend. The whole code in this repository is from my work. You are free to contribute and help to make the tool better.

Please see the Running example section above to get a link to a running instance of this web application.

What I have learned?

I have learned a lot about the open source world. It was my first real open source experience. I discovered how many open source projects there is out there, the communities around them, how people are working together to produce such good projects. I really enjoyed that and I definitively want to continue this journey.

I also learned many things related to OpenStreetMap/Mapbox and many projects build around them. But in a more general way I have learned a lot on the map systems. How maps are working, how vector tiles work, what are tiles servers, how maps are rendered, etc.

I worked on C++ without that much of experience with it. It was needed when I developed the clustering-vt module. It was not an easy step as I used libraries from the mapbox C++ ecosystem and I was not familiar with it at all. I dived into the source code of these libraries and learned many things. It made me want to use C++ more and get better with it, I am really happy that it happened.

It was the first time that I was setting up continuous integration and the first time I used github actions. This is so helpful.

And of course I learned a lot more about python development, PostgreSQL, YAML etc.

What to do next

I want to keep maintaining the Nominatim Data Analyser and Nominatim Data Analyser Frontend.

Issues have been opened on the repositories especially for the analyser concerning what currently needs to be done in order to improve the tool.

The main things to do currently are the following:

  • Add a multithreading feature to make the analyser run way faster as what takes the most time to execute are the PostgreSQL queries and the vector tiles generation (external clustering-vt module).
  • Add tests and documentation to the clustering-vt module and to the frontend code.
  • Optimize the clustering-vt algorithm to make it runs faster.
  • Add a “report as false positive” feature to the tool.

I would like to thank my mentors: Sarah Hoffmann (lonvia) and Marc Tobias (mtmail) who have helped me a lot for this project. It was amazing working with them and I hope we can continue like this in the future, for the QA tool but also for Nominatim and other projects too.

I would also like to thank Jochen Topf (joto) who developed osmoscope-ui which we used a lot initially and which was very helpful to develop our own web app. Jochen is also one of the authors of mapbox/vtzero which is the library I used to encode vector tiles to the .mvt/pbf format in the clustering-vt module.

Of course I would also like to thank the whole OpenStreetMap and Mapbox community for their work.

The end

Thank you for reading this post to the end. I hope you enjoyed it and I hope you will enjoy the new Nominatim QA Tool!

Blog Draft

dim 22 aoû 2021 - 17:39

lorem ipsum

weeklyOSM 578

dim 22 aoû 2021 - 11:57


count addr:housenumber nodes across all EU member states, broken down by country, will run in 30 seconds on an Overpass development branch [1] map data © OpenStreetMap contributors

  • A long thread on how to tag recreational routes designed for multiple transport modes led Kevin Kenny to suggest that striving for a Platonic ideal of tagging is not necessary.
  • oh8mxl wrote a blog post about ‘how to check cycling mapping mistakes and fixme tags in your area’.
  • Requests have been made for comments on the following proposals:
    • A new role ‘transfer’ for recreational route relations. There is no wiki page but you can find the mail list thread here.
    • cadet=military for mapping the meeting place of a local military cadet unit.
    • club=cadet for mapping the meeting place of a local youth cadet group.
  • Voting is underway for the following proposal:
  • Voting has ended for the following proposals:
    • cultivated=no/semi/fully to add sub-tags to natural=scrub was unsuccessful with 25 votes for, 18 votes against and 2 abstentions.
    • barrier=cycle_barrier to extend the tagging for cycle barriers was approved with 31 votes for, 2 votes against and 0 abstentions.
  • OSMF Board member Amanda is now up-to-date with their activity report for the month of July.
  • Discussions about using Discourse to replace the OSM forum have been happening
    for some time. The French community has migrated their forum from phpBB to Discourse and also migrated > all the existing posts from the old system. On the German forum, the question is raised > how to deal with old posts (for example: NL > 60,000, RU > 260,000 and DE > 300,000) when migrating from
  • User mariotomo took a detailed look at the projects hosted on the HOT Tasking Manager, gathering statistics on how many have been started, how many have finished, and how long they have been active.
  • In an email from MSF, GIS officer Roxana Nazarie outlined a planned way to share non-sensitive data collected and approved by field teams with OSM. The context is that the import process is too long-winded when data needs to be shared for a rapid response. Most replies suggested that the proposed method was an import anyway, and a number of other approaches were suggested.
  • Attila Kun and Brian Sperlongano are proposing an import of West Virginia State Forests.
OpenStreetMap Foundation
  • The draft Etiquette Guidelines, proposed by the Local Chapters and Communities Working Group Moderation Subcommittee, are open for comments until Wednesday 8 September. They will apply to the talk and osmf-talk mailing lists. However, the authors recommend applying them to all OSMF-run platforms (forum, wiki, and national mailing lists) as well. Comments can be written and reviewed on the discussion page.
  • In the streetscape map of Neukölln you can see how streets, sidewalks and street-side parking can be represented with OSM data. Tobias Jordans describes > in his blog post which data is visualised and where it comes from.
  • Dirk Brockmann invited people who want a global view of the COVID-19 situation to check out this visualisation.
  • Ashley Pinner and Harry Wood discussed, on Twitter, how various OSM maps show railway platforms.
Open Data
  • Since 2018 the UK government has been lavishly funding the Geospatial Commission, or at least their contractors: predominantly, management consultancies. It is therefore somewhat of a surprise that their recently published list of geospatial data from trustworthy organisations seems to have lots of gaps. Peter Wells spotted, that the report not only fails to mention OSM at all, but deems that there is no authoritative source of addresses for most of the country.
  • สุทธิสาร ปานสัสดี reflects > on a wide variety of licensing options in the context of OSM. He asks for feedback.
  • Yash Srivastava gave a final update, illustrated with screenshots, about his Google Summer of Code Project. The Nominatim Feedback Reporter will allow users to submit OpenStreetMap search (Nominatim) errors. These can then be added as test cases by the developers.
  • [1] User mmd demonstrated how a query to count addr:housenumber nodes across all EU member states, broken down by country, will run in 30 seconds on an Overpass development branch version. ATTENTION: The same query will not run on current production versions.
  • OrganicMaps (an OSM-based mobile app) has started a donation campaign to help pay for servers and fund development.
  • User mahdi1234 published a short article on building a Matrix chatbot to report statistics from taginfo in the Czech community channel
Did you know …
  • … about the Swiss cartographer Eduard Imhof? Our historical map-related item of the week. He was a pioneer of creating maps with shaded relief (as aspect of which we featured last week), and author of an influential text book. He also created, with skilled technical assistants, a number of large scale relief models, some of which can be seen in the Swiss Alpine Museum in Bern.
  • … you can keep up to date with the happenings in the OSM software world with Walter Nordmann’s software watchlist?
  • … about Pascal’s website Unmapped Places? This tool shows place tags that don’t have a road within 700 m of them, suggesting the presence of an unmapped settlement.
Upcoming Events Where What Online When Country 潍坊市 OpenStreetMap(中国大陆)第一次线下聚会 2021-08-20 – 2021-08-30 Amsterdam OSM Nederland maandelijkse bijeenkomst (online) 2021-08-21 Bogotá Distrito Capital Resolvamos notas de Colombia creadas en OpenStreetMap 2021-08-21 Clay County OpenStreetMap World Discord Summer mapathon ✓ 2021-08-21 – 2021-08-22 Bremen Bremer Mappertreffen (Online) ✓ 2021-08-23 105. OSM-Stammtisch Viersen und Umgebung 2021-08-24 Derby East Midlands OSM Pub Meet-up : Derby 2021-08-24 Zürich Missing Maps Zürich Mapathon 2021-08-25 Düsseldorf Düsseldorfer OSM-Treffen (online) 2021-08-25 Asia Pacific Map and Chat Hour 2021-08-27 [Online] OpenStreetMap Foundation board of Directors – public meeting 2021-08-27 Autrans-Méaudre en Vercors WikiCamp L’Escandille 2021-08-28 – 2021-08-29 Bogotá Distrito Capital Resolvamos notas de Colombia creadas en OpenStreetMap 2021-08-28 Hlavní město Praha Missing Maps CZ Mapathon 2021 #5 2021-08-31 cz San Jose South Bay Map Night ✓ 2021-09-03 Kurmin Musa Community Webinar: Local OSM community building: Tips, tricks and challenges 2021-09-03 ng Fortaleza Encontro de usuários OSM do Ceará, Brasil. 2021-09-04 京田辺市 京都!街歩き!マッピングパーティ:第26回 一休寺 2021-09-04 jp Greater London Missing Maps London Mapathon 2021-09-07 Landau an der Isar Virtuelles Niederbayern-Treffen ✓ 2021-09-07 Stuttgart Stuttgarter Stammtisch (Online) 2021-09-07 OpenStreetMap Michigan Meetup 2021-09-09 Nordrhein-Westfalen OSM-Treffen Bochum (September) 2021-09-09

If you like to see your event here, please put it into the OSM calendar. Only data which is there, will appear in weeklyOSM.

This weeklyOSM was produced by Nakaner, SK53, Sammyhawkrad, TheSwavu, derFred.

نگاه به گذشته

dim 22 aoû 2021 - 10:01

حوالی ۶ ماه میگذره که به طور فعال و رسمی یکی از مشارکت کنندگان این نقشه هستم.چیزهای زیاد در این مسیر یاد گرفتم و هنوز کلی چیز دیگه وجود داره که لازمه یاد بگیرم. با امکانات حداقلی به این کار ادامه میدم البته خوب میشد اگه امکانات بهتری داشتم ولی خب چه میشه کرد.یکی از دلایلی که شروع به این کار کردم علاقم و همچنین اینکه به عنوان یکی از استفاده کنندگان، دلم میخواد وقتی چیزی رو جستجو میکنم مخصوصا در وقت نیاز،برام نشون داده بشه و این عامل خودش محرک بزرگیه برای من امیدوارم که بتونم روز به روز بیشتر فعال باشم و کمکی باشم برای جامعه OSM

Aufruf - Hausnummern für Bad Neuenahr

dim 22 aoû 2021 - 9:52

AIch habe einen Kontakt in das Helferzentrum in Walporzheim und die brauchen eine Karte mit den Gebäuden und Hausnummern.

Ich habe gesehen, das in weiten Bereichen des Überschwemmungsgebiet diese fehlen.

Vielleicht fühlen sich einige aus der Umgebung angesprochen und können unterstützen.

Mittelfristig könnten die Hausnummern auch noch für die anderen betroffenen Orte im Ahrtal von Interesse werden.

Ich kümmere mich weiter um die Karten bis ich ab 3.9.2021 terminlich verhindert bin.

Bei der Gelegenheit können die wenigen notes gleich noch behoben werden.

My Favorite Places on the Map (now on the wiki)

sam 21 aoû 2021 - 22:28

I’ve created a small wiki user-page for my favorite places on OSM at User:Unkn0wnKevin/Favorite_Places.

Feel free to copy the source code to your own user page and drop me a message with a link, so I can check out your favorite places!

Invading Finland

sam 21 aoû 2021 - 19:20

We spent 7 days of vacation in Helsinki. Stop. First time in Finland. Stop. Very comfortable temperature. Stop. Lots of cute houses. Stop. Lots of bike paths. Stop. We just got back to Milan. Stop. In Finland we argued with my partner because she explained something about a new astonishing suitcase but I didn’t listen. Stop. It seems I was completely absorbed in mapping out a Finnish ramp for disabled people. Stop. Obviously this is not possible even if StreetComplete says I’m 26th in Finland. Stop. She still loves me. Stop.

Deriving River Network using QGIS,SRTM and OpenStreetMap

sam 21 aoû 2021 - 19:13

The article represents the method I have used to generate a stream network in a high altitude region in Kerala. The stream network of Devikulam in Munnar is the selected study area and stream and basin is generated using some tools available in QGIS. I am using SRTM DEM with a 30m resolution clipped to the study area and a set of SAGA tools available.

The steps are as follows:

  1. Load the DEM and reproject using the Warp/reprojection tool

The first step is to clip and reproject a DEM into a projected coordinate system.

Use the option, Raster > Project > Warp/Reproject

Select the required Projected coordinate system with reference to the study area.

  1. Fill Sinks in the reprojected DEM

This step is done to correct any unusual distortions of the DEM and to obtain a continuous hydrological network.

Here I am using Fill sinks, SAGA algorithm

Firstly, In settings ensure that SAGA tools are enabled.

From the processing toolbar > search and select Fill sinks(Wang & Liu) tool

Save the file and this filled DEM will be used for further processing.

3.Generating Strahler order streams

To get an idea about the existing order of the stream network, we can generate a reference layer using the Strahler order. This will give a clearer picture of Primary, Secondary and feeder streams and their hierarchy based on the principle of Strahler Stream Order

From the processing toolbox > Select Strahler Order

This will generate a raster file with stream networks Use the symbology feature to style the river streams for better visualization.

4.Generating vector channel network

To generate vector network of channels and drainage basins

From Processing toolbar > select the SAGA tool > Channel network and drainage basins tool

The threshold value will determine the detailing of the stream. ie. to decrease the value for a more detailed stream and vice versa.

Now we have the stream network and drainage basins

By default, the attribute table of the generated shapefile contains the fields: stream order, length of the stream etc.

5.Visualization using Hillshade

For better visualization, we can overlay a hillshade layer with our stream channels generated.

This will give a better perception of the area.

Go to Raster > Analysis > Hillshade, and overlay the stream channel

Identifying missing streams in Openstreetmap

The next most important step is to identify the data gaps in OpenStreetMap. We can do this by comparing the streams we generated using SRTM DEM and existing stream networks in OSM. The streams can either be extracted from OSM using specific tags and values from overpass-turbo or using the QGIS plugin QuickOSM

  1. Generating Buffer

Firstly load the extracted stream network from OSM and reproject the layer to a projected coordinate system. The reprojected files are used to create buffers.

To create buffer choose, Vector > Geoprocessing tool > Buffer

Apply a Buffer distance of 100 meters to both the OSM Channel and SRTM Channel.

  1. To find the incorrect or missing stream we can apply the Difference tool

From Vector > Geoprocessing tool > Difference

First, take input layer - OSM stream, Overlay layer as SRTM stream 100-meter Buffer

The process will give an output with consecutive Incorrect streams

Secondly, take input layer - SRTM Stream and, Overlay layer as OSM stream 100-meter Buffer

The results will give Missing streams

A logical comparison of the resulting layers will give us an idea about the data gaps in OSM. This can be identified and later hand-drawn using any OSM editors.


sam 21 aoû 2021 - 15:37

 私のOSMの編集回数がついに100回を突破しました。これからも編集に努めていきます。  現在は、主に佐伯市の建物、道路、公共交通機関などの編集を行っております。  しかしさすがに1人では足りません。暇のある方、佐伯についてご存知の方はぜひご協力をお願いいたします。  そしてこれからもよろしくお願いいたします。