One hot July evening ten years ago, I found my way to a bar somewhere near the Barbican in London and descended down the stairs into the basement space for the MapSwipe launch party. At the door I was handed my name sticker and asked to fill in the number of square kilometres I had already swiped on the app. I duly filled in my 597 sq km and joined the party.

MapSwipe is an open-source mobile app where you swipe through satellite imagery and help identify features. The app was created as part of the Missing Maps project to help solve a problem we had in the early days. Mappers like myself would be asked to map an area to help a humanitarian project but we would open task after task with very little in it to actually map. So, the simple, but genius, idea behind MapSwipe is what if volunteers could do a first pass through the area and pick out the features that need to be mapped; then this smaller area could be presented to mappers to trace the data and add it to OpenStreetMap.

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**On Tuesday 2nd of August I gave a short talk to the crowd at the London Missing Maps Mapathon about my experiences of being a validator. I had a scruffy piece of paper with some bullet points scribbled on it so this is my attempt to translate some of what I said that evening into a post.**

It feels pretty special to be standing up here tonight. In August two years ago (2014) I came along to my first mapathon with no experience of HOT, OSM, or any of the tools we’ve been using tonight: ID editor or JOSM. I started mapping with tracing lots of buildings, like tonight’s task, but in Sierra Leone and Liberia. This was at the time of the Ebola outbreak in West Africa and there was a lot of mapping to be done.

I started mapping with ID editor but after a couple of months I saw people near me using JOSM and was interested enough to download it and try it out at the mapathons. There was lots of help around and as I got comfortable using JOSM I got asked whether I’d consider doing some validation too. And I, perhaps foolishly, said I’d give it a go.

So how does validation fit into Missing Maps? Well, first off validators are volunteers too. If you’ve been to the Missing Maps website you will have seen this graphic showing the steps in the process starting with remote mappers, it then getting added to by community volunteers, and the third step where the data is used by humanitarian organisations. Validation is part of the remote mapping process, we’re very much a part of what is going on tonight.

The validation is there to provide a second pair of eyes and improve confidence of the end users in the whole process.

So what we actually do? It’s everything from looking to see all the buildings in a square are mapped and the roads labelled correctly to sense-checking the work on a square level and also a regional level. As we have already seen quite a few squares in different countries we’re aware through hard experience of some of the pitfalls in mapping.

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