OK, some progress.

I dredged up an old revision that I thought was working, and sure enough it still works.

It seems that offsetting a map by referring to it this way ‘7-LaghuPlan-midP3@Laghu‘ gives the result I want.

But inserting that map inside another map, with no other additions, referring to it now as ‘LaghuPlanMap-2’ breaks the offset map-connection hierarchy.

I feel like this should offer me some insight, and a path to some solution.  But it is not hitting me yet, unless it is somehow associated with map-levels?

It seems to make it difficult to generate a pattern that allows unlimited levels of offsetting, preferring instead to terminate at two levels, as in the Therion Book example.

Or is there a creative solution?

Details below…

Offset of offset – map-connection is submap to submap – looks good so far – rev 47.1.1

map LaghuPlanMap -title "Laghu Cave Plan, Mt Arthur"

    9-LaghuPlan-surface@Laghu #entrance pit

    LaghuPlanMap-1 [-050 000] below #top level offset map

    Laghu

endmap LaghuPlanMap

 map LaghuPlanMap-1

    9-LaghuPlan-underground@Laghu

    7-LaghuPlan-upperP1P2@Laghu

    7-LaghuPlan-midP2P3@Laghu

7-LaghuPlan-midP3@Laghu        [000 020] below #same as LaghuPlanMap-2, but with correct map-connections

              # LaghuPlanMap-2 [000 020] below        #referring to it this way breaks the map-connections

# if both above lines uncommented, then the map is unchanged, it still plots correctly

endmap

# map LaghuPlanMap-2

              # 7-LaghuPlan-midP3@Laghu

# endmap

Offset of offset – selected map to submap – breaks map-connection

map LaghuPlanMap -title "Laghu Cave Plan, Mt Arthur"

    9-LaghuPlan-surface@Laghu #entrance pit

    LaghuPlanMap-1 [-050 000] below #top level offset map

    Laghu

endmap LaghuPlanMap

 map LaghuPlanMap-1

    9-LaghuPlan-underground@Laghu

    7-LaghuPlan-upperP1P2@Laghu

    7-LaghuPlan-midP2P3@Laghu

# 7-LaghuPlan-midP3@Laghu     [000 020] below #same as LaghuPlanMap-2, but with correct map-connections

              LaghuPlanMap-2 [000 020] below        #referring to it this way breaks the map-connections

endmap

 map LaghuPlanMap-2

              7-LaghuPlan-midP3@Laghu

endmap

Thanks

Bruce