JervStrava heat map vs a fog of war map
They look similar and answer opposite questions. One shows where you go often and fades; the other shows everywhere you have ever been and does not. Which you want depends on what you are trying to see.
If you have used Strava for a while you have seen your personal heat map: your routes drawn over a city, the ones you repeat glowing brighter than the ones you did once. It is one of the nicest things in the product, and it is often the reason people go looking for a fog of war map — the two look alike at a glance.
They are not the same thing, and the difference is not cosmetic.
A heat map is about frequency
A heat map's brightness is a function of how often you go somewhere. Your commute is a hot line. A route you ran twice last spring is a faint one. Somewhere you went once, three years ago, is effectively invisible.
That is the correct design for what a heat map is for. It answers where do I usually go? — which is genuinely useful for spotting that you have run the same six roads for eight months, or for finding the segment you always take without thinking about it.
It also means a heat map is a moving picture. Take three months off and it dims. Move house and your old neighbourhood slowly disappears.
A fog of war map is about coverage
A fog of war map does not have brightness. A square is open or it is closed, and once it is open it stays open forever. Going somewhere a hundred times looks exactly the same as going once.
That makes it useless for spotting habits and very good at the question a heat map cannot answer: where have I actually been? Not this season — ever.
The practical difference shows up immediately. On a heat map, running your usual loop feels productive. On a fog map it changes nothing at all, and the only way to move the picture is to go somewhere new. People find this reorients their routes within about a week.
What each one rewards
- Heat map: consistency. Repetition makes the picture stronger.
- Fog map: novelty. Only new ground counts, and there is a finite amount of it near you.
Neither is better. They are opposite incentives, and which one you want depends on whether you are training or exploring. Plenty of people want both, and there is no reason not to run both — Strava for the training, something else for the map.
Where first footers come in
There is one thing a personal heat map structurally cannot do, and it is the reason fog of war maps get competitive.
A heat map is yours alone. A fog map, if the app compares yours against everyone else's, knows something extra: which squares nobody has opened. The first person through a square can be recorded as the first person through it, permanently.
Jerv calls those first footers. It turns an evening walk into something with a small, real stake attached, and it sends people down streets they have driven past for years. Strava's global heatmap shows you where the crowd goes; this is the inverse — it shows you where it does not.
The honest summary
If you want to know whether you are training enough, and where, use the heat map you already have. It is good and it is free with an account you already own.
If you want a permanent record of everywhere you have ever been — one that does not fade when you take a winter off, and that makes the unexplored parts of your own city visible — that is what a fog of war map app is for.
Jerv is one, it is free, and it does not need your Strava account. Get the iPhone beta — it is open to anyone through TestFlight — or open the web app and watch the map start blacked out. The Android beta opens soon.