Using Structuremap With Mapping Cards - Lowrance HDS Gen3 Operator's Manual

You can create standard or high resolution files. High resolution .smf
files capture more detail, but take longer to convert and are larger
than standard resolution files.
To save disc space it is recommended to remove the StructureScan
(*.sl2) files after conversion.

Using StructureMap with mapping cards

StructureMap allows you to maintain full chart capability and can be
used with embedded cartography as well as Navionics, Insight and
other third-party charting cards compatible with the system.
When using StructureMap with mapping cards, copy the
StructureMap (.smf ) files to the unit's internal memory. We
recommend keeping copies of StructureMap files on external
microSD cards.
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StructureMap | HDS Gen3 Operator Manual