Even the most modern charting material is often based on 100 year old depth data measure with a pole from a moving rowing boat. Distances were measured with a watch while rowing the boat at constant velocity. Mathematical models are used to generate depth curves for the area between the sparse measurement points.
For a good reason all producers of marine instruments and charting plotters have a disclaimer. No hardware or software product is error free. GPS data can be error prone and unreliable at times. Wireless connections transfering the data can be disturbed at the most stressful moments. Charts and electronic charts contain errors.
New efforts are being made to correct many of those errors. Flight and satellite pictures are being used and find islands as far as 100m from their actually charted position.
But for many seasons the Swedish transport authorities also asked for help to localize those in order to reduce these dangerous differences to the official charts. You can even win a price for the "best rock". Everyone here knows a couple of shallow waters and underwater rocks not found on any chart. Often you find these rocks even far of the coast, surrounded by "deep-enough" water.
Don't rely on the electronic charts, don't rely on the wireless router for navigation.
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