Bruce Mutton wrote extensive information on this topic in Bruce's Data Structure. But there are a few details, I think, that should be noted.

The standard convention when drawing a map is to follow the surveys and related sketches. But in Therion you are absolutely free:

• One scrap may be connected with stations from several surveys. Just because such a scrap is more logical for the map definitions.
• Maps are independent from the survey structure too: you may define maps as you need to create logical, easily understandable maps.
• You may define as many maps based on one survey set as you want; from a map including only one scrap to complex maps of systems and areas.
• You may define a map which contains two nearby scraps from two different caves if they are in one survey structure just to look for possible connection.
• You may divide a long, slanting, tunnel intersecting three horizontal levels, into three scraps and define a map which follows the horizontal structure or a map which contains only those three scraps of that slanting tunnel.

The main condition is the command “select” in the “thconfig” file which defines which map definition to use. A simple way how to write such “select” commands is to double-click on the name of the required map in the “Map structure” section on the right/left side of the “Compiler window”.

Hint: Always define map(s) and use the “select” command in thconfig!