Over the passed year, the Belgian community was involved in organizing 10 mapathons. It is an incredibly easy thing to do, once you have the documentation in order. And once you realize you should do as little as possible - just find people who have a location and a recruiting network.
Some time ago, Pascal Neis wrote an article about new mappers recruited through classic channels, Maps.me and humanitarian mapping. I asked and got a changeset dump of all the people who participated in our mapathons.
Here's some stats about that.
Overal, 1925 unique mappers participated in our mapathons, of which 328 were new mappers.
First, did we manage to turn them into returning mappers? Well... As could have been predicted by Pascal's depressing numbers: not really. The data used was from December 2016. You can clearly see that the percentage having more than one mapping day drops as we approach December. That simply means you need to wait a bit before you can do a decent analysis.
Say we give people 3 months, then we only look at the edits from September and before. We got 23% percent of people to map more than once! 10% mapped 3 days or more. Unfortunately, that's even slightly worse than the international average. Maybe we just worked for a more difficult audience :)
We usually tell people to map something in their own neighborhood before starting on the mission. Less than 21 of them did so. And in fact, only 4 of the 328 have more than one Belgian mapping day. As a comparison, we had 2059 people mapping for the first time in Belgium in 2016.
Even if that all sounds thoroughly depressing, it should be noted that organizing mapathons still is a great way to build a community, even if it doesn't show in these numbers. The mapathon movement was crucial in turning mappers into organizing volunteers. Especially the two interuniversity mapathons (with 200 participants last year and over 300 this year) are momentum-building moments. For the State of the Map in Brussels, we somehow managed to recruit 20 Belgian mappers to help out. That would have been impossible without the mapathons.
Apart from that, the constant confrontation with people who don't have any idea about OpenStreetMap, is a stark reminder that we should all keep up the missionary work.