Organised Editing/Activities/Madagascar Itasy lake Mapathon

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Mapathon of Itasy lake, Madagascar


Since 2007, Itasy region (Madagascar) and Nouvelle Aquitaine region (France) have been establishing a multi-purposes cooperation partnership in order to build up Itasy internal capacities and develop methodologies, tools (including a geoportal) and actions to handle some issues faced by the Malagasy region. The Declic sub-project aims at finding ways to relieve the current over-fishing in the lake and the health issues related to bilharzia. This requires data regarding both population, road accessibility and hydrography. Three Tasking Manager jobs had been created in the instance (#5517, #5519, #5520) in the past and some mapping activities had been done, but most of the data was still incomplete.

Early April, a two-weeks long training camp organized by Organisation Internationale de la Francophonie (OIF) about OSM and Free geomatics tools have started at Campus Numérique Francophone (CNF) in Antananarivo (as described here), with 30 Malagasy beneficiaries and 5 advanced trainers (3 Malagasy, 1 Togolese and 1 French). This training format encompasses both daily mapping and a specific full-day long mapathon. The training team welcomed the request of Itasy/Nouvelle Aquitaine team to support their OSM data needs by dedicating the planned mapathon to the #5520 existing job.


You can contact alternatively:

or sent any question or request to the public and archived talk-mg discussion list.


The hashtag #hotosm-project-5520 comes automatically with the edits.


The mapping activities start April 17, 2019 and continue until April 27. The mapathon occurs April 19.

Tools and Data Sources

JOSM is the only used editor, along with standard aerial imagery (mostly Bing for being the clearer one + DG Standard imagery for complements as it is a bit more recent) as well as OpenCycleMap rendering for its contours lines, in order to facilitate the riverways editing. Tagging scheme follows general use or specific ones for the context, especially Highway_Tag_Africa


Our core and support team of active and experienced OSM mappers:

The other mappers are the training camp beneficiaries (mixing mainly Governmental Institutions, Development organizations and Geography students) + a few members of OSM MG community who joined the mapathon.


All participants have already at least a 4 days OSM experience when the mapathon occurs. The core team regularly checks every mapper editions, provides both personal and general guidance by showing common or specific issues and ways to handle them.

Measuring the quality of data / clean up

This mapping project is not a quick-and-fire mapathon with absolute beginners. Data quality is at heart of this mapping project, following the steps below.

During the mapathon each completed task is:

  • analyzed with JOSM Validator and corrected consequently if required
  • filtered to make visible thematic completeness or illogical tagging (eg for highways) and facilitate corrections or complements

Every completed task is then analyzed by the core team, following the classical Tasking Manager steps, both during and after the mapathon. The core team organizes two consecutive mornings of tasks validation + goes deeper in the quality check : larger areas are validated in order to consolidate the data at smaller scale, especially the road network, to make it fully routable (eg no highway=unclassified connected to tracks or paths at both ends). It is downloaded for checking using Overpass, in order not to overcharge the OSM API.

[Osmose] will also be used to identify and correct remaining mistakes.


Here is a screenshot of Pascal Neis' OSM changeset analysis tool over Lake Itasy mapped area, dated April 23, 2019 Pascal Neis' OSM changeset analysis tool over Lake Itasy, dated April 23, 2019

Here is a screenshot of Osmose, dated June 6, showing that there is no highly severe error detected over Lake Itasy mapped area Some results will be posted here after the mapping is over.

Here is a screenshot of Osmose, dated June 6, 2019, showing that there is no highly severe error detected over Lake Itasy mapped area

This link directs to the same area in Osmose.