Field notes 5 MIN READ
What a heatmap of your year actually shows
Not a statistic. Three hundred routes drawn on top of each other, where the roads you use become dark and the once-in-a-lifetime trip stays faint.
A heatmap sounds like a statistic. It is not. It is the least processed thing we draw.
It is just the routes, stacked
Take every activity. Draw each one as a line at low opacity. Where you have ridden a road fifty times, fifty faint lines land on top of each other and the road goes dark. Where you went once, one faint line stays pale.
There is no binning, no grid, no density calculation. The image is the evidence.
This matters because the alternative — dividing the map into cells and colouring by how many points fall in each — smooths away exactly what you want to see. A grid tells you *roughly here*. Stacked lines tell you *this junction, this side of the road, this way round the roundabout*.
What it ends up looking like
Three things, always.
A knot. Wherever you start from. Every route leaves the same door, so the first kilometre is the darkest thing on the sheet. This is also the thing we trim, for reasons that are obvious once stated.
Spokes. The handful of roads out of town that are actually pleasant. There are never as many as you think.
One or two long threads. The trip to the coast. The week away. Faint, because it happened once, and structurally important because it is the only part of the picture that is not routine.
The framing problem
A single exceptional ride wrecks the scale. If everything you do is within 40 km of home and one ride went 220 km, fitting all of it puts your entire training in a small knot in one corner.
We drop activities whose extent is far outside the median before choosing the frame. That is not tidying the data — it is what the word *heatmap* means. It is a picture of where you train, not of everywhere you have been.
Why the trim is not optional here
One route reveals a home once. Three hundred routes reveal it three hundred times, and every one of them converges on the same doorstep — the darkest pixel on the sheet is your address.
We cut a radius off both ends of every track before anything is drawn. On a single print that is a courtesy. On a heatmap it is the difference between a portrait of your year and a map to your house.
Questions people actually ask
- Is a heatmap a calculated density map?
- No. It is the routes themselves, drawn semi-transparently on top of each other. Roads ridden fifty times get fifty faint lines and go dark; a road ridden once stays pale. That is more honest than binning points into a grid, and it is what your training actually looked like.
- How many activities do you need?
- Around thirty before the pattern reads. Below that it looks like a tangle. Above two hundred the shape of a town appears.
- Why does my big summer trip barely show?
- Because it is one line among hundreds, and because a single long trip stretches the frame. A ride twice as far as everything else pulls the scale out until the daily routes shrink to a knot.
- Do indoor sessions appear?
- No. An indoor session has no route, so it contributes nothing. A winter of trainer rides leaves a thinner map than the winter felt.
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