Tap a summit in HiiKER and you’ll sometimes see a small (est) after its height. It means exactly what it looks like: that number is an estimate, and we’d rather tell you than let you assume it was surveyed.
Here’s where it comes from.
Two ways we know how high a mountain is
Every peak in HiiKER gets its height one of two ways.
The first is a surveyed figure. Somebody — a national mapping agency, a surveyor, a mapper with a good GPS and patience — has measured the summit and recorded it in OpenStreetMap. When that figure exists, we use it, and we show it plainly with no label. It’s the best answer available.
The second is a terrain model. Plenty of summits have never had a height recorded against them. There are a lot of hills in the world and not many surveyors. For those, we sample a digital elevation model — a DEM — and show what it says. That’s the number we mark with (est).
What a DEM actually is
A digital elevation model is a giant grid laid over the world, with one ground height stored in each cell. Most of the global ones come from radar or stereo imagery collected by satellites and space shuttle missions.
The important part is the grid. In the models that cover the whole planet, each cell is roughly 30 metres square. That cell holds one height for the entire 30-by-30 patch of ground beneath it.
For a valley floor or a broad moor, that’s fine. One number describes the whole square pretty well.
Why summits are the hard case
A summit is, by definition, the highest single point in the area. And a grid cell doesn’t store the highest point in its square — it stores something closer to the average across it.
So on a sharp peak, the cell containing the summit is pulled down by all the ground sloping away on every side. The real top is usually a little above what the model says. The pointier the mountain, the bigger the gap. A broad, flat-topped hill barely suffers; a rocky spike can be out by a fair margin.
A few other things nudge the number around:
- Radar doesn’t always reach the ground. On forested slopes it can return from the tree canopy, reading high. On snowfields it reads the snow, which moves with the season.
- Steep ground is noisy. Cliffs and gullies are exactly where these models are least reliable.
- The summit may not be centred in its cell. If the true top sits near a cell edge, the sample can land on ground several metres lower.
In practice, an (est) height on a rounded hill is usually within a few metres. On a steep, rocky summit it can be more. It’s a good number. It isn’t a surveyed one.
It doesn’t affect your peak bagging
This is the part worth being clear about: the height has nothing to do with whether you bagged the peak.
Peak bagging in HiiKER works on position. When your recording passes close enough to a summit’s location, you’ve bagged it (how close counts). The height shown on the sheet is there for interest — it isn’t a threshold you have to cross, and an estimate that’s three metres low has never cost anyone a summit.
The same goes for your totals, your lists and your leaderboard placings. All of it runs on where you walked, not on how high we think the hill is.
Help us make them surveyed
Because our surveyed heights come from OpenStreetMap, anyone can improve them — and the fix reaches every hiker, not just you.
If you know a summit’s real height, add or correct the ele tag on that peak in OpenStreetMap. Next time our data refreshes, that peak stops being an estimate in HiiKER, and the (est) label disappears on its own.
It’s one of the nicer things about building on open data: a correction made once by one hiker quietly improves the map for everybody who walks there afterwards.