Wookey (2005-08-17) pointed out some problems with areas. Infact (M. Budaj) the use of areas should be reduced to a minimum, and replaced, whenever possible, with point symbols.

If is advisable to avoid areas splitted on two scraps. In that case one should put one area on each scrap, with a straight invisible border line (option "-subtype invisible") [thwiki 17] where the scrap ends, but there would still be coloring problems (for instance coloring the map with "altitude"). This notwithstanding, in caves with several pools and mud banks, areas splitted on two scrap are almost inevitable.

Another problem happens when you split a line which is part of the border of an area. The two new lines get new ids, while the area still contains the id of the old line (which does not exists any more). Therefore when the project is compiled with therion, there is an error like (here "l14-480--196" is the old id)

     object does not exist -- l14-480--196

A little help comes from xtherion: clicking on the error, it brings up the map editor with the problem causing area selected. You must go to the "Area control" to check the lines on the border of the area, and find that id. Unfortunately xtherion does not highlight the area in the canvas and it is not so easy to find the other lines of the border, and to fix the problem.

Another possibility is to search the id with the text editor open on the file listed on the error line.

The problem is that a graphical item, the id of which is referred by another item, is dropped leaving a dangling reference. This is a problem with xtherion, which should use reference counting techniques to keep into account the number of references to the objects. At a minimum xtherion should give a warning about deleting a referenced object ...

Probably a similar problem occurs with the "join" command. In this case the work of xtherion would be more difficult because a "join" connects item from different files, and the "join" appears in a file at a higher (logical) level. xtherion needs to have this higher-level file open to find whether the deleting item occurs in a "join".

Another problem is the "Show area" command of the "Area control". It is useful, but it seems that it shows only the lines of type "border", and not those of type "wall" or "contour".