To download a bathymetric map, you would need to be sure that your map is already uploaded to Lakebook.
In Lakebook, select the map that you want to export and click download:
Exported data appear in .CSV format that will contain such values as latitude, longitude, depth and a timestamp. Timestamp will appear as the number of milliseconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970. (UNIX Time)
Please note that GPS records latitude and longitude values approximately every second, thus you may see those data values indicated as 0 - which happens if the depth was recorded, but the coordinates were not. The sonar itself scans about 15 times per second, this is why most data lines are without coordinates.
It is only possible to export bathymetric data created in Boat or On-shore GPS modes of the sonar. Recordings made Standard and Ice Fishing modes will contain only the sonar data, which cannot be exported.