Going from ArcMap:
Load .shp into MapEdit
Shapefiles consist of two different types of trails (already polylines) and a shaded area for the borders of the park.
Add another level (already levels 1 and 2 which I assume are for the polygon and polylines)
Save as MP/TXT.
Export as Garmin IMG and I get this error:
Error E021: Grid definition for layers must be descending
solved by adjusting the level values.
Yes the levels and zooms need to be in order.