[asheshouse]

Have you thought about doing this map in stages?

Provided you start with a map_h which covers the entire area, and then crop out a section for your stage 1 map, you can complete the first section and get it issued.

Once the first stage is complete you can expand the map to pick up a larger area, using your master map_h to add the height data.

There's no need to start with the big map straight away.