Am i supposed to have "negative depth" in sea?

OsmAnd is an open source (GPLv3) map and navigation app for Android and iOS using OpenStreetMap for map data. OsmAnd has many features which help you at your journey: offline maps and navigation, trip recorder, ruler, mapillary, the online tracker, navigation for any profiles like a car, bicycle, public transport, boat, pedestrian, hiking and other. Using OsmAnd you get "the Swiss knife" among navigation apps. Offline maps of OsmAnd are updated every hour (OsmAnd Live feature).