Rijwind

I helped prepare an Openstreetmap mapping party recently. Getting a group of people to map an area concurrently during an OpenStreetMap mapping party as efficiently as possible posed a challenge. Below I document a process with JOSM and Mapnik, which describes how OSM-data and a set of zones can be used to create a Map that allows people to choose, which part they are going to map. The choosing can happen several days before the event or on the day itself.

The resulting Mapnik map

• Download OSM-data of the area of interest in JOSM. And save that data locally
• Import the downloaded OSM-data into a postgres/postgis database with osm2pgsql
• Run Mapnik to render a OSM-base map
• Create a set of zones as separate Josm-layers. Determine the size of the zones depending on the expected amount of ways and mode of transportation of the mappers. Making more smaller zones is recommended, in case you cannot make much assumptions, but this means more workt. In short YMMV
• Save the JOSM-layers into several osm-datafiles for possible reuse
• In Josm merge the separate layer files into one OSM datafile
• Edit that layer datafile. Since all nodes and ways are marked as below 0. Just remove all the minus signs and your all set. Note: this data is not supposed to be uploaded but id’s of less than 0 means: new data for upload through the OSM API 0.5
• Now fill up the postgres database with only the zones
• Render this zone dataset to an image file
• Merge the two output images with an images editing program (The Gimp)

The script to render the prepared data to images looks like this:

OSM2PGSQL=/usr/local/src/osmapps/utils/export/osm2pgsql
ln -s $OSM2PGSQL/default.style
$OSM2PGSQL/osm2pgsql -c ../hoboken.osm
./set-mapnik-env ./generate_image.py
mv image.png
hoboken-osm.png $OSM2PGSQL/osm2pgsql -c ../overlay.osm
./set-mapnik-env ./generate_image.py mv image.png overlay.png


During the Mapping party this map was effectively used during the initial sitdown to assign everybody one or more zones. The limiting factor with this rendering is however, that this map is not practical for use during the actual mapping because the streetnames of the boundaries are missing.

Some ideas resulting from actually using this process:

• The points of the zone could transformed to a route (gpsbabel). Many units will probably allow for this, but need the possibility to show maps. The mapper should stay within this route during surveying

• Create separate Garmin maptiles with mkgmap based on the osm-data plus the zone files, possibly with an extra no-names layer and upload the maptiles with QLandkarteGT.

• Create proximity (.gpi) files for each zone and put it in a Garmin unit. This should theoratically trigger an alarm, also with hardware that does not support mapping.