LakeMap

LakeMap puts Switzerland's official lake surveys on your boat: depth contours, depth shading, seamarks, and harbours for 22 lakes — from Lake Zurich, Lake Constance, and Lake Lucerne to Lake Geneva, Lago Maggiore, and the Engadine lakes. Every chart ships inside the app and works with no connection at all; out on the water there is no loading spinner.

The crucial difference is the datum. Ordinary charts show depths against a fixed chart datum. LakeMap instead stores the absolute height of the lake floor and subtracts the current water level from the Swiss federal gauges (FOEN). The depth you see is today's depth — at low autumn levels just as after snowmelt.

From position, course, and speed (Kalman-smoothed COG/SOG) the app projects a course cone 60 seconds ahead and warns in four tiers with distinct tones before the bottom comes up. Unsurveyed water is explicitly treated as a hazard: zones without depth data render violet and raise their own alert tier instead of falsely looking safe — the whole data pyramid is built so that every coarser answer errs on the safe side.

On top of that: harbour and buoy search, a depth-aware route planner that avoids shallows and respects the shore-zone rules of the Swiss inland navigation ordinance, track recording of the trip you sailed, and a watch mode that keeps the alert live in the background. The weather view shows hourly wind and gust forecasts per lake from the MeteoSwiss ICON models — cached offline with visible age, with cues at the official Swiss storm-warning thresholds (strong wind from 25 kn, storm from 33 kn) and official warnings for your lake.

LakeMap runs without an account, without ads, and without tracking; position and tracks stay on the device. The chart packs come from a purpose-built Python/GDAL pipeline that turns swisstopo swissBATHY3D into vector and raster tiles plus a shoal-conservative height pyramid. LakeMap is not an official navigational aid — official charts and the shore storm-warning lights remain authoritative.