I reached out to Nukemap’s creator, Alex Wellerstein, to talk about the site’s creation, how people have used it for the last decade, and what he’s seen change in the last week. Wellerstein is a historian of science and nuclear weapons and a professor at the Stevens Institute of Technology. Seriousness of the subject matter aside, it’s one of my favorite interviews in a while. The conversation has been lightly edited for clarity.

Charlie Warzel: Let’s start at the beginning—over a decade ago now—why’d you build Nukemap?

Alex Wellerstein: There’s the true story and the one that makes me look more rational and smart. Let’s start with the one that makes me look smart. I recognized that it’s difficult to conceptualize the size of nuclear weapons. I have a very hard time dealing with numbers and visualizing them and translating these equations into code that makes a visualization allows me to better understand these weapons for my job.

The real story, which is more haphazard, is that I first created a visualization tool for this a long time ago, back in 2004, before Google Maps. I used a terrible series of screenshots of MapQuest and it was a mess. I didn’t have the technology to do what I wanted.

That changed in 2012. I had started a blog, and as you, a content creator, know well, you need content! I was investigating a totally different nuke project, which required drawing circles to show nuclear radii. And in the process I realized the code had matured and what was hard to do in 2004 was trivial in 2012. I figured I’d bang it and some of my fellow academics and policy people would find it interesting. I didn’t imagine it’d get seen by the general public. I built it in the course of a weekend and I sent it to some colleagues and gave it a terrible name—something like Alex’s Amazing Nuclear Weapon Simulator. Everyone told me that name was awful, so I changed it to Nukemap.

Warzel: Did it take off right away?

Wellerstein: Not quite. It got a little traffic from my blog. My blog is about the history of nuclear weapons, so we’re not talking about tons of traffic here. But then, somehow, the U.K. tabloids picked it up and wrote a terrible story about this new viral nuke tool that was so scary. Nukemap hadn’t gone viral but, as I learned then, a story about something going viral can make it go viral. I got tons of traffic, and that made me take the project more seriously. [I figured] if this is a tool for other people, then I should probably spend more than two days working on it. So I upgraded the features, gave the code an overhaul, made fallout models and casualties models, all by 2013. And that’s where it is now, basically. For better or worse it’s the most engaged-with thing I’ve ever done. So far, about 40 million people have used it. It’s been a key part of my career and likely led to the job I have now.

Warzel: It’s always the things you don’t expect that have the biggest impact online, I find.

Wellerstein: I can come up with reasons why Nukemap works but ultimately some of this is idiosyncratic. If the U.K. tabloids don’t pick it up, does it get to this level of popularity? Now it is high in the search results for how big is a nuclear explosion? With algorithms and social media, the more attention you get the more you’re going to get. It becomes self-building.