How many empty homes are there in your city?

• Most cities across Europe have a big number of empty homes. Some may not be usable (but maybe can refurbished), some may be second residences, but many could be put to good use as social or public housing or even simply pushed into the housing market, increasing supply and hopefully helping reduce the number of people who can't afford a decent home.

• But in all those cases the first step is to know how many empty homes are there and, ideally, to map them: who they belong to, where exactly they are, how long they have been empty and why...

• Now, counting and mapping empty homes can be notoriously tricky because, to start with, different authorities legally and institutionally define "empty homes" in different ways.

• Then, you need yourself a workable definition of "empty home" when you are gathering data; and depending on your methodology you need a way to verify the data, for example if you are compiling it through crowdsourcing; and if you want to keep your database live instead than as a snapshot, then you need ways to keep it updated.

• That is why empty homes is a prime topic to be covered by collaborative research and journalism, and don't hesitate to get in touch with us at the Arena Housing Project if you would like to know more or to join efforts to work on this issue.