I Used Strava’s New Heat Map to Find a Stranger’s Home Address

The running and cycling app Strava has many features to help you find new running routes, including segments, a route builder and a global heat map. Earlier this summer, Strava began offering a weekly heat map. It’s great for finding trails and routes that are popular at the moment, but may reveal information that’s more sensitive than what you thought Strava users might see.

Using the weekly heatmap, I was able to scan the map, select an area that seemed to have one active runner, and find that person’s name and location. To be clear, this person is a stranger to me and I chose the area at random; It took mere minutes to find this information. If you live in a big city, you may not have to worry about this, but if you’re in a rural or suburban area, you might want to check your privacy settings. More on these settings below, but first I want to explain what happens with the new card.

What is Strava’s weekly heat map?

Strava offers a range of mapping tools to help you find places to run or ride. Only paid subscribers can zoom out to street level.

As Strava explains here , the weekly heat map is updated every week, aggregating data from activities (such as running and cycling) that are set to “All.” There’s been a global heat map for a long time, but it only tells you which routes are generally popular. The weekly heat map gives you a real-time view of where people are going now . For example, I could use this during icy or muddy times of year to see which county park trails are still walkable despite the weather.

The problem is that if you’re browsing in less populated areas, like many rural and suburban areas, there’s a pretty serious privacy issue: If you’re the only person running in your area lately, your tracks will be the only ones. which appear on the weekly map. (On a global map, by contrast, they would blend in with everyone who drives on these roads throughout the year.)

How a Weekly Heat Map Can Highlight Your Lonely Running Routes

That’s what I mean. I’ve been running almost every day lately, and most of my runs are in the neighborhood around my house. When I saw the weekly heat map feature, I immediately zoomed in on a nearby park to check out popular trails. But when I returned to where my house is, my own running routes stood out as cloudy blue lines.

This is very different from what the global heat map shows. My running slightly darkens the lines on the global heat map, but another person wouldn’t be able to tell my personal running habits just by looking at them.

But the weekly heat map is a completely different story. It looks like I and maybe one other person have a couple of favorite roads in my area. Sometimes I run in circles up and down a certain road; this road shines brighter than the rest.

Zooming out, I can see other areas where there is clearly one person with a favorite route. I can even switch between the global heat map and the weekly heat map and make observations like: “The person who runs [route A] has been using it a lot lately, but his neighbor, who seems to start and end at [location B], is doesn’t.” I wasn’t active. Do I know these people? Not at all. But I think I know at least one of their names.

Heat maps and local legends may reveal more than you realized.

The weekly heat map becomes especially interesting when combined with Strava’s other core social feature: Segments . A segment is a route with a name and leaderboard. Let’s say there is a difficult hill in your area; maybe someone decided it was worthy of a leaderboard, so they created a segment called Neighborhood Hill that goes up that hill.

Using Strava’s map tool , you can click on a segment and see who has the fastest time, as well as who the local legend is – the person who has run it the most in the last 90 days.

So, as an experiment, I scrolled through the map and chose an area far from me, along a route that one or at most a few people often drive: a thin, cloudy blue line crossing only a few roads, with no activity. on other nearby roads.

I then asked the map to show me segments in the same area, and sure enough, the route included a named segment. I clicked on the segment and it turned out that only three people had viewed it in the last 90 days. Two of them ran it once; the other ran it repeatedly.

This last person – Local Legend – will most likely be the one who ran this blue cloud route (or collection of routes) last week. I looked at the ends of this cloud line and decided that there was a good chance that LL (as I’ll call them) lives in one of the houses closest to one of these end points. To satisfy my curiosity, I looked through county real estate records for houses on this street. And heck, one of the houses at the end of that cloudy blue line belongs to a man with the same first and last name as our Local Legend.

I wouldn’t be able to achieve this level of accuracy using just the global heat map or just the segments. I might have been able to guess that LL lived nearby, but I had no idea which road, much less which house to look for. But the weekly heat map led me straight to their home.

How to remove your data from the weekly heat map

If your account is completely locked and everything is set to private, your data is not used here. But if parts of your runs or rides are visible to everyone (which is necessary if you want to compete on segments), your data is part of a weekly heat map. Here are some ways to change this:

• Strava says that activities set to “only you” or “followers” are excluded from the map. However, these types of activities do not fall into the lists of segment leaders. (You can read Strava’s explanation of privacy settings here .)

• Strava also lets you automatically hide the start and end points of your activities. This will allow you to run from your home to the nearest park, with part of the run in the park being public and part of the run near your home not. Read about how to set this up here . Again, the private portion does not appear on the weekly heat map and will not be eligible for participation in the segment leaderboards. Hiding the start and end points will help avoid the scenario described above, in which I was able to track a person to a specific house. But that doesn’t change the fact that a stranger can guess that you often take a certain route.

• Another partial solution is to change your name and profile picture so that they do not contain any identifying information. This will make it harder for your friends to recognize you on Strava, so not everyone will want to do it (social activity is part of Strava).

• Finally, there is a setting that will remove your data from global and weekly heatmaps . (It’s a shame they don’t have two separate settings.) Go to Settings, then Privacy Controls, and scroll to Map Visibility. There is a checkbox that says “Contribute your activity data to anonymized aggregate data sets.” Uncheck this box.

And yes, Strava considers this information “anonymous,” although, at least in some cases, it’s trivial to associate it with your name. That’s the nature of large data sets: they contain small, identifiable pieces far more frequently than the people collecting the data might realize. For example, the Census Bureau intentionally adds noise (variation) to the data sets it releases publicly as a form of “disclosure avoidance.” This is a known problem in large data sets, but Strava’s main method for now to avoid disclosure is to ask users to change their privacy settings if they don’t want them turned on. It’s not enough in my opinion, but at least now you know where to find these settings.

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