#3 - Senegal, consolidated mapping, Base Roads Check

amara kourouma marked #69 as done

Jean-Marc Liotier marked #256 as done

Jean-Marc Liotier marked #217 as done

SeverinGeo marked #78 as done

SeverinGeo marked #97 as done

SeverinGeo marked #101 as done

Getting a thematic, consolidated data over a territory is one of the main concerns for OSM, that often confronts very detailed areas and very partially mapped areas, as in Senegal. The state of completeness and consistency is totally unknown.

This project uses a methodology to get a consolidated mapping over a territory, designed first for the Central African Republic. It uses a buffer made from an exisiting reference road layer.

This project aims at completing, checking and enhancing the accuracy of the road network over CAR using 500 m wide buffers from the DCW (Digital Chart of the World) road layer dated 2009, that is public domain and considered as a reference layer.

It will also allow to differentiate the road sections for which the geometry is accurate (because they are covered by high resolution imagery) from inaccurate ones, due to low resolution imagery. The latter will be identified through a specific attribute that will differentiate them easily. Knowing the roads source and date to create the geometry is important for the humanitarian organizations using the OpenStreetMap data as one of the sources to get the best possible road network for their internal uses.

Every task is one road section is the combination of Digitized Landsat, Russian Topos and gROADS. As and when this job is over, the achievement status of OpenStreetMap data compared to this reference will be known through the percentage bar.

Created by SANA Ibrahim - Updated - Priority: medium


Entities to Map
routes, zones résidentielles, noms de lieux
Changeset Comment
Senegal, Base Roads Check, #llgtm-tache-3
When saving your work, please leave the default comment but add what you actually mapped, for example "added buildings and a residential road".

Using JOSM? Please use the dedicated preset.

This mapping project does not fit with iD. A specific preset has been designed for JOSM and can be downloaded from the link just above. The following instructions provide also the right tags to be used.

Select and lock a tile then load it as usual in JOSM.

  1. The aim is going from one end to another and edit or enhance the road if needed. Please work at a close scale: the scale bar should be under 50m. The best tool to improve the accuracy of a way is in JOSM and can be easily activated by pressing the "W" key. For a demo in video, click here.

  2. When starting, put a source= tag with the name of the imagery then check the date of this imagery with a right click, then "Show tile info" in the contextual menu and look at the Capture date. Add source=Bing and source:date= informing the year or put unknown if there is no year mentioned. Check this video to visualize the process.

  3. Afterwards, when it is obvious that the imagery had changed (different colors), check its date and, if needed, cut the road and change the year as the value of the source:date key. Check this video to visualize the process.


if the downloaded area do not cover the whole extent of the road section

  • then add the missing part with an extra, manual download. Check this video to visualize the process.

if the area to be downloaded is too large and rejected by the server

  • then download the .gpx file as proposed above, open it in JOSM, stretch the right panel to keep for the map only the necessary width, then download with the Mirror Download plugin. Once downloaded you can put the right panel to its original width. Check this video to visualize the process.

if the area is no more covered by a high resolution imagery and there is no available accurate trace

  • then cut the road where the high resolution imagery ends and add a fixme=low accuracy tag on the section without high resolution imagery. Check this video to visualize the process. If the road cannot be completed even coarsely, then cut the section, just before the road cannot be traced anymore and change the tag for fixme=cannot be completed for the smaller section just before the gap. Check this video to visualize the process.

if the road crosses a road that has been not yet mapped

  • then please digitize the first 5-10 first nodes and add the following tags: highway=unclassified and fixme=unfinished, so that it will be possible afterwards to identify and complete them. Check this video to visualize the process.

if you cross a residential area and/or a place that has not been mapped yet.

  • then either trace them, or add a node with a fixme tag like fixme=name+residential area. Check this video to visualize the process.

Once all this is done, mark the task as done.

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